Outputs from `swift build -v` and `swift build -v -Xcxx -v`

1.swift-build-v.log

/usr/bin/xcrun --sdk macosx --show-sdk-platform-path
/usr/bin/xcrun --sdk macosx --find xctest
/Applications/Xcode-beta.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/swiftc -print-target-info
xcrun vtool -show-build /Applications/Xcode-beta.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/swift/pm/4_2/libPackageDescription.dylib
/Applications/Xcode-beta.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/swiftc -L /Applications/Xcode-beta.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/swift/pm/4_2 -lPackageDescription -Xlinker -rpath -Xlinker /Applications/Xcode-beta.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/swift/pm/4_2 -target x86_64-apple-macosx10.15 -swift-version 5 -I /Applications/Xcode-beta.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/swift/pm/4_2 -sdk /Applications/Xcode-beta.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.16.sdk -package-description-version 5.3.0 /Users/jonaszaugg/Documents/Projects/BoostTest/Package.swift -o /var/folders/p6/54pvrv0j32gf4h2vvjgdbk680000gn/T/TemporaryDirectory.Ke4Oee/boosttest-manifest
/var/folders/p6/54pvrv0j32gf4h2vvjgdbk680000gn/T/TemporaryDirectory.Ke4Oee/boosttest-manifest -fileno 7 sandbox-exec -p '(version 1)
(deny default)
(import "system.sb")
)
'
xcrun --sdk macosx --show-sdk-platform-path
xcrun vtool -show-build /Applications/Xcode-beta.app/Contents/Developer/Platforms/MacOSX.platform/Developer/Library/Frameworks/XCTest.framework/XCTest
xcrun --sdk iphoneos --show-sdk-platform-path
xcrun vtool -show-build /Applications/Xcode-beta.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/Library/Frameworks/XCTest.framework/XCTest
xcrun --sdk appletvos --show-sdk-platform-path
xcrun vtool -show-build /Applications/Xcode-beta.app/Contents/Developer/Platforms/AppleTVOS.platform/Developer/Library/Frameworks/XCTest.framework/XCTest
xcrun --sdk watchos --show-sdk-platform-path
xcrun vtool -show-build /Applications/Xcode-beta.app/Contents/Developer/Platforms/WatchOS.platform/Developer/Library/Frameworks/XCTest.framework/XCTest
/Applications/Xcode-beta.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/clang -fobjc-arc -target x86_64-apple-macosx10.10 -isysroot /Applications/Xcode-beta.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.16.sdk -F /Applications/Xcode-beta.app/Contents/Developer/Platforms/MacOSX.platform/Developer/Library/Frameworks -g -O0 -DSWIFT_PACKAGE=1 -DDEBUG=1 -fblocks -index-store-path /Users/jonaszaugg/Documents/Projects/BoostTest/.build/x86_64-apple-macosx/debug/index/store -fmodules -fmodule-name=CWrapper -I /Users/jonaszaugg/Documents/Projects/BoostTest/Sources/CWrapper/include -I /Users/jonaszaugg/Documents/Projects/BoostTest/Sources/CXXLib/include -fmodule-map-file=/Users/jonaszaugg/Documents/Projects/BoostTest/.build/x86_64-apple-macosx/debug/CXXLib.build/module.modulemap -fmodules-cache-path=/Users/jonaszaugg/Documents/Projects/BoostTest/.build/x86_64-apple-macosx/debug/ModuleCache -MD -MT dependencies -MF /Users/jonaszaugg/Documents/Projects/BoostTest/.build/x86_64-apple-macosx/debug/CWrapper.build/src/wrapper.cpp.d -c /Users/jonaszaugg/Documents/Projects/BoostTest/Sources/CWrapper/src/wrapper.cpp -o /Users/jonaszaugg/Documents/Projects/BoostTest/.build/x86_64-apple-macosx/debug/CWrapper.build/src/wrapper.cpp.o
/Applications/Xcode-beta.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/clang -fobjc-arc -target x86_64-apple-macosx10.10 -isysroot /Applications/Xcode-beta.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.16.sdk -F /Applications/Xcode-beta.app/Contents/Developer/Platforms/MacOSX.platform/Developer/Library/Frameworks -g -O0 -DSWIFT_PACKAGE=1 -DDEBUG=1 -fblocks -index-store-path /Users/jonaszaugg/Documents/Projects/BoostTest/.build/x86_64-apple-macosx/debug/index/store -fmodules -fmodule-name=CXXLib -I /Users/jonaszaugg/Documents/Projects/BoostTest/Sources/CXXLib/include -fmodules-cache-path=/Users/jonaszaugg/Documents/Projects/BoostTest/.build/x86_64-apple-macosx/debug/ModuleCache -MD -MT dependencies -MF /Users/jonaszaugg/Documents/Projects/BoostTest/.build/x86_64-apple-macosx/debug/CXXLib.build/src/boosttest.cpp.d -c /Users/jonaszaugg/Documents/Projects/BoostTest/Sources/CXXLib/src/boosttest.cpp -o /Users/jonaszaugg/Documents/Projects/BoostTest/.build/x86_64-apple-macosx/debug/CXXLib.build/src/boosttest.cpp.o
/Applications/Xcode-beta.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/swiftc -module-name BoostTest -incremental -emit-dependencies -emit-module -emit-module-path /Users/jonaszaugg/Documents/Projects/BoostTest/.build/x86_64-apple-macosx/debug/BoostTest.swiftmodule -output-file-map /Users/jonaszaugg/Documents/Projects/BoostTest/.build/x86_64-apple-macosx/debug/BoostTest.build/output-file-map.json -c /Users/jonaszaugg/Documents/Projects/BoostTest/Sources/BoostTest/main.swift -I /Users/jonaszaugg/Documents/Projects/BoostTest/.build/x86_64-apple-macosx/debug -target x86_64-apple-macosx10.10 -swift-version 5 -enable-batch-mode -index-store-path /Users/jonaszaugg/Documents/Projects/BoostTest/.build/x86_64-apple-macosx/debug/index/store -sdk /Applications/Xcode-beta.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.16.sdk -F /Applications/Xcode-beta.app/Contents/Developer/Platforms/MacOSX.platform/Developer/Library/Frameworks -I /Applications/Xcode-beta.app/Contents/Developer/Platforms/MacOSX.platform/Developer/usr/lib -L /Applications/Xcode-beta.app/Contents/Developer/Platforms/MacOSX.platform/Developer/usr/lib -Onone -enable-testing -g -j4 -DSWIFT_PACKAGE -DDEBUG -Xcc -fmodule-map-file=/Users/jonaszaugg/Documents/Projects/BoostTest/.build/x86_64-apple-macosx/debug/CWrapper.build/module.modulemap -I /Users/jonaszaugg/Documents/Projects/BoostTest/Sources/CWrapper/include -Xcc -fmodule-map-file=/Users/jonaszaugg/Documents/Projects/BoostTest/.build/x86_64-apple-macosx/debug/CXXLib.build/module.modulemap -I /Users/jonaszaugg/Documents/Projects/BoostTest/Sources/CXXLib/include -module-cache-path /Users/jonaszaugg/Documents/Projects/BoostTest/.build/x86_64-apple-macosx/debug/ModuleCache -parseable-output
/Applications/Xcode-beta.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/swift -frontend -c -primary-file /Users/jonaszaugg/Documents/Projects/BoostTest/Sources/BoostTest/main.swift -emit-module-path /Users/jonaszaugg/Documents/Projects/BoostTest/.build/x86_64-apple-macosx/debug/BoostTest.build/main~partial.swiftmodule -emit-module-doc-path /Users/jonaszaugg/Documents/Projects/BoostTest/.build/x86_64-apple-macosx/debug/BoostTest.build/main~partial.swiftdoc -emit-module-source-info-path /Users/jonaszaugg/Documents/Projects/BoostTest/.build/x86_64-apple-macosx/debug/BoostTest.build/main~partial.swiftsourceinfo -emit-dependencies-path /Users/jonaszaugg/Documents/Projects/BoostTest/.build/x86_64-apple-macosx/debug/BoostTest.build/main.d -emit-reference-dependencies-path /Users/jonaszaugg/Documents/Projects/BoostTest/.build/x86_64-apple-macosx/debug/BoostTest.build/main.swiftdeps -target x86_64-apple-macosx10.10 -enable-objc-interop -sdk /Applications/Xcode-beta.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.16.sdk -I /Users/jonaszaugg/Documents/Projects/BoostTest/.build/x86_64-apple-macosx/debug -I /Applications/Xcode-beta.app/Contents/Developer/Platforms/MacOSX.platform/Developer/usr/lib -I /Users/jonaszaugg/Documents/Projects/BoostTest/Sources/CWrapper/include -I /Users/jonaszaugg/Documents/Projects/BoostTest/Sources/CXXLib/include -F /Applications/Xcode-beta.app/Contents/Developer/Platforms/MacOSX.platform/Developer/Library/Frameworks -enable-testing -g -module-cache-path /Users/jonaszaugg/Documents/Projects/BoostTest/.build/x86_64-apple-macosx/debug/ModuleCache -swift-version 5 -Onone -D SWIFT_PACKAGE -D DEBUG -enable-anonymous-context-mangled-names -Xcc -fmodule-map-file=/Users/jonaszaugg/Documents/Projects/BoostTest/.build/x86_64-apple-macosx/debug/CWrapper.build/module.modulemap -Xcc -fmodule-map-file=/Users/jonaszaugg/Documents/Projects/BoostTest/.build/x86_64-apple-macosx/debug/CXXLib.build/module.modulemap -target-sdk-version 10.16 -module-name BoostTest -o /Users/jonaszaugg/Documents/Projects/BoostTest/.build/x86_64-apple-macosx/debug/BoostTest.build/main.swift.o -index-store-path /Users/jonaszaugg/Documents/Projects/BoostTest/.build/x86_64-apple-macosx/debug/index/store -index-system-modules
/Applications/Xcode-beta.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/swift -frontend -merge-modules -emit-module /Users/jonaszaugg/Documents/Projects/BoostTest/.build/x86_64-apple-macosx/debug/BoostTest.build/main~partial.swiftmodule -parse-as-library -sil-merge-partial-modules -disable-diagnostic-passes -disable-sil-perf-optzns -target x86_64-apple-macosx10.10 -enable-objc-interop -sdk /Applications/Xcode-beta.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.16.sdk -I /Users/jonaszaugg/Documents/Projects/BoostTest/.build/x86_64-apple-macosx/debug -I /Applications/Xcode-beta.app/Contents/Developer/Platforms/MacOSX.platform/Developer/usr/lib -I /Users/jonaszaugg/Documents/Projects/BoostTest/Sources/CWrapper/include -I /Users/jonaszaugg/Documents/Projects/BoostTest/Sources/CXXLib/include -F /Applications/Xcode-beta.app/Contents/Developer/Platforms/MacOSX.platform/Developer/Library/Frameworks -enable-testing -g -module-cache-path /Users/jonaszaugg/Documents/Projects/BoostTest/.build/x86_64-apple-macosx/debug/ModuleCache -swift-version 5 -Onone -D SWIFT_PACKAGE -D DEBUG -enable-anonymous-context-mangled-names -Xcc -fmodule-map-file=/Users/jonaszaugg/Documents/Projects/BoostTest/.build/x86_64-apple-macosx/debug/CWrapper.build/module.modulemap -Xcc -fmodule-map-file=/Users/jonaszaugg/Documents/Projects/BoostTest/.build/x86_64-apple-macosx/debug/CXXLib.build/module.modulemap -target-sdk-version 10.16 -emit-module-doc-path /Users/jonaszaugg/Documents/Projects/BoostTest/.build/x86_64-apple-macosx/debug/BoostTest.swiftdoc -emit-module-source-info-path /Users/jonaszaugg/Documents/Projects/BoostTest/.build/x86_64-apple-macosx/debug/BoostTest.swiftsourceinfo -module-name BoostTest -o /Users/jonaszaugg/Documents/Projects/BoostTest/.build/x86_64-apple-macosx/debug/BoostTest.swiftmodule
/Applications/Xcode-beta.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/swiftc -sdk /Applications/Xcode-beta.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.16.sdk -F /Applications/Xcode-beta.app/Contents/Developer/Platforms/MacOSX.platform/Developer/Library/Frameworks -I /Applications/Xcode-beta.app/Contents/Developer/Platforms/MacOSX.platform/Developer/usr/lib -L /Applications/Xcode-beta.app/Contents/Developer/Platforms/MacOSX.platform/Developer/usr/lib -lc++ -L /Users/jonaszaugg/Documents/Projects/BoostTest/.build/x86_64-apple-macosx/debug -o /Users/jonaszaugg/Documents/Projects/BoostTest/.build/x86_64-apple-macosx/debug/BoostTest -module-name BoostTest -emit-executable -Xlinker -rpath -Xlinker @loader_path @/Users/jonaszaugg/Documents/Projects/BoostTest/.build/x86_64-apple-macosx/debug/BoostTest.product/Objects.LinkFileList -Xlinker -rpath -Xlinker /Applications/Xcode-beta.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/swift/macosx -target x86_64-apple-macosx10.10 -Xlinker -add_ast_path -Xlinker /Users/jonaszaugg/Documents/Projects/BoostTest/.build/x86_64-apple-macosx/debug/BoostTest.swiftmodule -L /Applications/Xcode-beta.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib

2.swift-build-v-Xcxx-v.log

/usr/bin/xcrun --sdk macosx --show-sdk-platform-path
/usr/bin/xcrun --sdk macosx --find xctest
/Applications/Xcode-beta.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/swiftc -print-target-info
xcrun vtool -show-build /Applications/Xcode-beta.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/swift/pm/4_2/libPackageDescription.dylib
/Applications/Xcode-beta.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/swiftc -L /Applications/Xcode-beta.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/swift/pm/4_2 -lPackageDescription -Xlinker -rpath -Xlinker /Applications/Xcode-beta.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/swift/pm/4_2 -target x86_64-apple-macosx10.15 -swift-version 5 -I /Applications/Xcode-beta.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/swift/pm/4_2 -sdk /Applications/Xcode-beta.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.16.sdk -package-description-version 5.3.0 /Users/jonaszaugg/Documents/Projects/BoostTest/Package.swift -o /var/folders/p6/54pvrv0j32gf4h2vvjgdbk680000gn/T/TemporaryDirectory.mzj7GS/boosttest-manifest
/var/folders/p6/54pvrv0j32gf4h2vvjgdbk680000gn/T/TemporaryDirectory.mzj7GS/boosttest-manifest -fileno 7 sandbox-exec -p '(version 1)
(deny default)
(import "system.sb")
)
'
xcrun --sdk macosx --show-sdk-platform-path
xcrun vtool -show-build /Applications/Xcode-beta.app/Contents/Developer/Platforms/MacOSX.platform/Developer/Library/Frameworks/XCTest.framework/XCTest
xcrun --sdk iphoneos --show-sdk-platform-path
xcrun vtool -show-build /Applications/Xcode-beta.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/Library/Frameworks/XCTest.framework/XCTest
xcrun --sdk appletvos --show-sdk-platform-path
xcrun vtool -show-build /Applications/Xcode-beta.app/Contents/Developer/Platforms/AppleTVOS.platform/Developer/Library/Frameworks/XCTest.framework/XCTest
xcrun --sdk watchos --show-sdk-platform-path
xcrun vtool -show-build /Applications/Xcode-beta.app/Contents/Developer/Platforms/WatchOS.platform/Developer/Library/Frameworks/XCTest.framework/XCTest
/Applications/Xcode-beta.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/clang -fobjc-arc -target x86_64-apple-macosx10.10 -isysroot /Applications/Xcode-beta.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.16.sdk -F /Applications/Xcode-beta.app/Contents/Developer/Platforms/MacOSX.platform/Developer/Library/Frameworks -g -O0 -DSWIFT_PACKAGE=1 -DDEBUG=1 -fblocks -index-store-path /Users/jonaszaugg/Documents/Projects/BoostTest/.build/x86_64-apple-macosx/debug/index/store -fmodules -fmodule-name=CWrapper -I /Users/jonaszaugg/Documents/Projects/BoostTest/Sources/CWrapper/include -I /Users/jonaszaugg/Documents/Projects/BoostTest/Sources/CXXLib/include -fmodule-map-file=/Users/jonaszaugg/Documents/Projects/BoostTest/.build/x86_64-apple-macosx/debug/CXXLib.build/module.modulemap -fmodules-cache-path=/Users/jonaszaugg/Documents/Projects/BoostTest/.build/x86_64-apple-macosx/debug/ModuleCache -v -MD -MT dependencies -MF /Users/jonaszaugg/Documents/Projects/BoostTest/.build/x86_64-apple-macosx/debug/CWrapper.build/src/wrapper.cpp.d -c /Users/jonaszaugg/Documents/Projects/BoostTest/Sources/CWrapper/src/wrapper.cpp -o /Users/jonaszaugg/Documents/Projects/BoostTest/.build/x86_64-apple-macosx/debug/CWrapper.build/src/wrapper.cpp.o
/Applications/Xcode-beta.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/clang -fobjc-arc -target x86_64-apple-macosx10.10 -isysroot /Applications/Xcode-beta.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.16.sdk -F /Applications/Xcode-beta.app/Contents/Developer/Platforms/MacOSX.platform/Developer/Library/Frameworks -g -O0 -DSWIFT_PACKAGE=1 -DDEBUG=1 -fblocks -index-store-path /Users/jonaszaugg/Documents/Projects/BoostTest/.build/x86_64-apple-macosx/debug/index/store -fmodules -fmodule-name=CXXLib -I /Users/jonaszaugg/Documents/Projects/BoostTest/Sources/CXXLib/include -fmodules-cache-path=/Users/jonaszaugg/Documents/Projects/BoostTest/.build/x86_64-apple-macosx/debug/ModuleCache -v -MD -MT dependencies -MF /Users/jonaszaugg/Documents/Projects/BoostTest/.build/x86_64-apple-macosx/debug/CXXLib.build/src/boosttest.cpp.d -c /Users/jonaszaugg/Documents/Projects/BoostTest/Sources/CXXLib/src/boosttest.cpp -o /Users/jonaszaugg/Documents/Projects/BoostTest/.build/x86_64-apple-macosx/debug/CXXLib.build/src/boosttest.cpp.o
Apple clang version 12.0.0 (clang-1200.0.22.8)
Target: x86_64-apple-macosx10.10
Thread model: posix
InstalledDir: /Applications/Xcode-beta.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin
Apple clang version 12.0.0 (clang-1200.0.22.8)
Target: x86_64-apple-macosx10.10
Thread model: posix
InstalledDir: /Applications/Xcode-beta.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin
ignoring nonexistent directory "/Applications/Xcode-beta.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.16.sdk/usr/include/c++/v1"
 "/Applications/Xcode-beta.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/clang" -cc1 -triple x86_64-apple-macosx10.10.0 -Wdeprecated-objc-isa-usage -Werror=deprecated-objc-isa-usage -Werror=implicit-function-declaration -emit-obj -mrelax-all -disable-free -disable-llvm-verifier -discard-value-names -main-file-name wrapper.cpp -mrelocation-model pic -pic-level 2 -mthread-model posix -mframe-pointer=all -fno-strict-return -fno-rounding-math -masm-verbose -munwind-tables -faligned-alloc-unavailable -target-sdk-version=10.16 -target-cpu core2 -dwarf-column-info -debug-info-kind=standalone -dwarf-version=2 -debugger-tuning=lldb -target-linker-version 607.2 -v -resource-dir /Applications/Xcode-beta.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/clang/12.0.0 -index-store-path /Users/jonaszaugg/Documents/Projects/BoostTest/.build/x86_64-apple-macosx/debug/index/store -dependency-file /Users/jonaszaugg/Documents/Projects/BoostTest/.build/x86_64-apple-macosx/debug/CWrapper.build/src/wrapper.cpp.d -skip-unused-modulemap-deps -MT dependencies -sys-header-deps -isysroot /Applications/Xcode-beta.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.16.sdk -F/Applications/Xcode-beta.app/Contents/Developer/Platforms/MacOSX.platform/Developer/Library/Frameworks -D SWIFT_PACKAGE=1 -D DEBUG=1 -I /Users/jonaszaugg/Documents/Projects/BoostTest/Sources/CWrapper/include -I /Users/jonaszaugg/Documents/Projects/BoostTest/Sources/CXXLib/include -I/usr/local/include -stdlib=libc++ -internal-isystem /Applications/Xcode-beta.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1 -internal-isystem /Applications/Xcode-beta.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.16.sdk/usr/local/include -internal-isystem /Applications/Xcode-beta.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/clang/12.0.0/include -internal-externc-isystem /Applications/Xcode-beta.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.16.sdk/usr/include -internal-externc-isystem /Applications/Xcode-beta.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/include -O0 -Wno-reorder-init-list -Wno-implicit-int-float-conversion -Wno-c99-designator -Wno-final-dtor-non-final-class -Wno-extra-semi-stmt -Wno-misleading-indentation -Wno-quoted-include-in-framework-header -Wno-implicit-fallthrough -Wno-enum-enum-conversion -Wno-enum-float-conversion -fdeprecated-macro -fdebug-compilation-dir /Users/jonaszaugg/Documents/Projects/BoostTest -ferror-limit 19 -fmessage-length 0 -stack-protector 1 -mdarwin-stkchk-strong-link -fblocks -fencode-extended-block-signature -fregister-global-dtors-with-atexit -fgnuc-version=4.2.1 -fmodule-name=CWrapper -fmodule-map-file=/Users/jonaszaugg/Documents/Projects/BoostTest/.build/x86_64-apple-macosx/debug/CXXLib.build/module.modulemap -fobjc-runtime=macosx-10.10.0 -fobjc-arc -fobjc-arc-exceptions -fcxx-exceptions -fexceptions -fmax-type-align=16 -fdiagnostics-show-option -o /Users/jonaszaugg/Documents/Projects/BoostTest/.build/x86_64-apple-macosx/debug/CWrapper.build/src/wrapper.cpp.o -x c++ /Users/jonaszaugg/Documents/Projects/BoostTest/Sources/CWrapper/src/wrapper.cpp
ignoring nonexistent directory "/Applications/Xcode-beta.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.16.sdk/usr/include/c++/v1"
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Both commands taken after swift package clean. Both commands compile the package without errors, yet both fail when a step is taken individually (e.g. line 20 of the first log). Individual steps can't find the Boost headers. What's crazy is that the first log never prints /usr/local/include (yet compiles) and the second one prints it due to the additional -Xcxx -v flags yet only with the verbose output of compiling C++ files which, also taken individually, cannot find the headers either because they don't know to search there.
I'm really going crazy here because I don't understand where -I/usr/local/include is set!