Windows support by Ruben Van Boxem.

llvm-svn: 142235
Cr-Mirrored-From: sso://chromium.googlesource.com/_direct/external/github.com/llvm/llvm-project
Cr-Mirrored-Commit: 073458b1ab5489dce6f2ec789889c377b690ccf4
diff --git a/include/thread b/include/thread
index ce3ca49..4366c41 100644
--- a/include/thread
+++ b/include/thread
@@ -100,7 +100,9 @@
 #endif
 #include <pthread.h>
 
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #pragma GCC system_header
+#endif
 
 #define __STDCPP_THREADS__ __cplusplus