Araq/Nim: Basic Objective-C FFI fails to compile on OS X

nim_objc_osx_error.nim

# For simplicity, doesn't use anything from Foundation, like NSObject or NSString.
# Just basic Objective-C FFI.

{.emit: """

@interface Foo
+ (void)bar;
@end

@implementation Foo
+ (void)bar {}
@end

""".}

proc fooBar {.importobjc: "Foo bar", nodecl.}

fooBar()

output.txt

$ nim objc --parallelBuild:1 --noNimblePath -r nim_objc_osx_error
Hint: used config file '/Users/philip/Nim/config/nim.cfg' [Conf]
Hint: system [Processing]
Hint: nim_objc_osx_error [Processing]
clang -c  -w  -I/Users/philip/Nim/lib -o nimcache/nim_objc_osx_error.o nimcache/nim_objc_osx_error.m
[Linking]
Undefined symbols for architecture x86_64:
  "__objc_empty_cache", referenced from:
      _OBJC_CLASS_$_Foo in nim_objc_osx_error.o
      _OBJC_METACLASS_$_Foo in nim_objc_osx_error.o
  "_objc_msgSend", referenced from:
      _nim_objc_osx_errorInit in nim_objc_osx_error.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)
Error: execution of an external program failed