Explicitly mark the pthread forward declarations as extern C

Summary: These were being mangled as C++ functions rather than C functions.

Reviewed By: yfeldblum

Differential Revision: D7462668

fbshipit-source-id: e4e83e16aafad3d888599dd78bdbb4ac2711ad7f

folly/portability/PThread.h

@@ -96,9 +96,11 @@ int pthread_setspecific(pthread_key_t key, const void* value);
 
 // Because we defined `INCLUDE_NP` above, the non-portable APIs don't actually
 // get declared. We still need them, so declare them ourselves instead.
+extern "C" {
 PTW32_DLLPORT HANDLE PTW32_CDECL
 pthread_getw32threadhandle_np(pthread_t thread);
 PTW32_DLLPORT DWORD PTW32_CDECL pthread_getw32threadid_np(pthread_t thread);
+}
 
 // And now everything else that isn't just here for `pid_t`.