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

folly/container/test/F14TestUtil.h

@@ -123,8 +123,7 @@ struct ThrowOnCopyTestInt {
 
   ThrowOnCopyTestInt() {}
 
-  __attribute__((__noreturn__))
-  ThrowOnCopyTestInt(const ThrowOnCopyTestInt& other)
+  [[noreturn]] ThrowOnCopyTestInt(const ThrowOnCopyTestInt& other)
       : x(other.x) {
     throw std::exception{};
   }