Example changes for automake to support x86 & arm64 plus universal binaries

gistfile1.txt

# configure.ac

# add an --enable-macos-universal-binary flag that when building for mac 
# create a universal x86_64 / arm64 binary
AC_ARG_ENABLE([macos-universal-binary],
    [AS_HELP_STRING([--enable-macos-universal-binary],
            [Create an universal x86_64+arm64 binary when building for macos)])],,
    [enable_macos_universal_binary=no])

# Determine if we're building for macos/darwin by checking for macos & darwin 
# in the build triple.
AC_CANONICAL_HOST
case $host_os in
  *macos*) macos="yes" ;;
  *darwin*) macos="yes" ;;
  *) macos="no" ;;
esac

# If building for Mac we will pass x86_64 or arm64 to the compiler based
# on user options or target type. 
AS_IF([test "$macos" = "yes"],[
  clang_arch_x86_64="no"
  clang_arch_arm64="no"

  # If building a universal binary ask clang for both
  AS_IF([test "$enable_macos_universal_binary" = "yes"],[
      clang_arch_x86_64="yes"
      clang_arch_arm64="yes"
  ],[
    # If building for x86_64 ask for that
    AS_IF([test "$host_cpu" = "x86_64"],[
      clang_arch_x86_64="yes"  
    ])
    # If building for arm64, ask for that
    AS_IF([test "$host_cpu" = "aarch64"],[
      clang_arch_arm64="yes"      
    ])
  ])    
  # set the defines for our makefile
  AM_CONDITIONAL([CLANG_ARCH_X86_64], [test "$clang_arch_x86_64" = "yes"])
  AM_CONDITIONAL([CLANG_ARCH_ARM64], [test "$clang_arch_arm64" = "yes"])     
], [
  # Just set these to false. They need to be present in the else clause to keep
  # automake happy.
  AM_CONDITIONAL([CLANG_ARCH_X86_64], [false])
  AM_CONDITIONAL([CLANG_ARCH_ARM64], [false]) 
])

# makefile.am

# Pass x86_64 in compiler and linker flags if asked
if CLANG_ARCH_X86_64
AM_CPPFLAGS += -arch x86_64
AM_CFLAGS += -arch x86_64
AM_CXXFLAGS += -arch x86_64
AM_LDFLAGS += -arch x86_64
endif

# Pass arm64 in compiler and linker flags if asked
# (Note - may be additive to the above)
if CLANG_ARCH_ARM64
AM_CPPFLAGS += -arch arm64
AM_CFLAGS += -arch arm64
AM_CXXFLAGS += -arch arm64
AM_LDFLAGS += -arch arm64
endif