Bundled libffi can't be compiled on clang

[Takashi Kato]

Seems like clang's assembler doesn't support some of directives. The followings are the log from Travis CI (OS X environment):

/Users/travis/build/ktakashi/sagittarius-scheme/sagittarius-0.6.7/ext/ffi/libffi-3.0.13/src/x86/unix64.S:45:2: error: unknown directive
 .type ffi_call_unix64,@function
 ^

/Users/travis/build/ktakashi/sagittarius-scheme/sagittarius-0.6.7/ext/ffi/libffi-3.0.13/src/x86/unix64.S:204:2: error: unknown directive
 .size ffi_call_unix64,.-ffi_call_unix64
 ^

/Users/travis/build/ktakashi/sagittarius-scheme/sagittarius-0.6.7/ext/ffi/libffi-3.0.13/src/x86/unix64.S:208:2: error: unknown directive
 .type ffi_closure_unix64,@function
 ^

/Users/travis/build/ktakashi/sagittarius-scheme/sagittarius-0.6.7/ext/ffi/libffi-3.0.13/src/x86/unix64.S:326:2: error: unknown directive
 .size ffi_closure_unix64,.-ffi_closure_unix64
 ^

/Users/travis/build/ktakashi/sagittarius-scheme/sagittarius-0.6.7/ext/ffi/libffi-3.0.13/src/x86/unix64.S:334:11: error: mach-o section specifier uses an unknown section type
 .section .eh_frame,"a",@progbits

Even though the bundled libffid is the fallback but it's better to have it working.

[Takashi Kato]

Seems like this is OS X specific. So we can't do anything for now.

[Takashi Kato]

Fixing OSX detection on bundled libffi (Fixes #143)

→ <<cset 387e55914b39>>