Fix most GCC attribute ignored warnings

llvm-svn: 267074
Cr-Mirrored-From: sso://chromium.googlesource.com/_direct/external/github.com/llvm/llvm-project
Cr-Mirrored-Commit: 89dd1dd2782de71d56c512e44b9dfda2f7b95351
diff --git a/include/thread b/include/thread
index c3eb437..bf5b8e8 100644
--- a/include/thread
+++ b/include/thread
@@ -219,7 +219,7 @@
 
 }  // this_thread
 
-template<> struct _LIBCPP_TYPE_VIS_ONLY hash<__thread_id>;
+template<> struct hash<__thread_id>;
 
 class _LIBCPP_TYPE_VIS_ONLY __thread_id
 {