[NFCI] Fix Wattributes warnings from Sema. (#157906)

See: #157834

There is some visibility concerns here, so this patch suppresses the
diagnostic. I believe we are doing this intentionally, so unless someone
comes up with a good reason we should either remove the visibility of
Sema, or make these types visible, this seems like the right way
forward.

Fixes: #157834

Author: erichkeane

clang/include/clang/Sema/Sema.h

@@ -845,9 +845,16 @@ enum AttrName { Target, TargetClones, TargetVersion };
 
 void inferNoReturnAttr(Sema &S, const Decl *D);
 
+#ifdef __GNUC__
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wattributes"
+#endif
 /// Sema - This implements semantic analysis and AST building for C.
 /// \nosubgrouping
 class Sema final : public SemaBase {
+#ifdef __GNUC__
+#pragma GCC diagnostic pop
+#endif
   // Table of Contents
   // -----------------
   // 1. Semantic Analysis (Sema.cpp)