Fix non-portable annotation syntax in F14TestUtil.h
Fix non-portable annotation syntax in F14TestUtil.h

Summary: [Folly] Fix non-portable annotation syntax in `F14TestUtil.h`, using portable `[[noreturn]]` v.s. non-portable `__annotation__((__noreturn__))`. The non-portable syntax works with GCC and Clang, but is not recognized by MSVC.

Reviewed By: jkedgar, terrelln, Orvid

Differential Revision: D16553166

fbshipit-source-id: a652d31d31eca773009885f648f44ea3798e1460

facebook/folly,facebook/folly,facebook/folly,facebook/folly,facebook/folly