Suppress Clang warning for dirfd() on OSX.
Suppress Clang warning for dirfd() on OSX.

In the OSX 10.10 SDK, dirfd() is a macro that uses a GNU statement expression.
NaCl compiles with -Wgnu-statement-expression. I added clang suppressions for
the warning around the code that calls dirfd().

BUG=https://code.google.com/p/chromium/issues/detail?id=555879

Review URL: https://codereview.chromium.org/1449153002

sbc100/native_client,sbc100/native_client,sbc100/native_client,sbc100/native_client,sbc100/native_client,sbc100/native_client