[clang][Sema] Don't warn for implicit uses of builtins in system headers

Signed-off-by: Sarnie, Nick <[email protected]>

Author: sarnex

clang/lib/Sema/SemaDecl.cpp

@@ -2376,9 +2376,14 @@ NamedDecl *Sema::LazilyCreateBuiltin(IdentifierInfo *II, unsigned ID,
     return nullptr;
   }
 
+  // Warn for implicit uses of header dependent libraries,
+  // except in system headers.
   if (!ForRedeclaration &&
       (Context.BuiltinInfo.isPredefinedLibFunction(ID) ||
-       Context.BuiltinInfo.isHeaderDependentFunction(ID))) {
+       Context.BuiltinInfo.isHeaderDependentFunction(ID)) &&
+      (!getDiagnostics().getSuppressSystemWarnings() ||
+       !Context.getSourceManager().isInSystemHeader(
+           Context.getSourceManager().getSpellingLoc(Loc)))) {
     Diag(Loc, LangOpts.C99 ? diag::ext_implicit_lib_function_decl_c99
                            : diag::ext_implicit_lib_function_decl)
         << Context.BuiltinInfo.getName(ID) << R;

clang/test/Sema/Inputs/builtin-system-header.h

@@ -0,0 +1 @@
+#define MACRO(x,y) _InterlockedOr64(x,y);

clang/test/Sema/builtin-system-header.c

@@ -0,0 +1,8 @@
+// RUN: %clang_cc1 -fms-extensions -fsyntax-only -verify -triple arm64-windows -isystem %S/Inputs %s
+
+// expected-no-diagnostics
+#include <builtin-system-header.h>
+
+void foo() {
+  MACRO(0,0);
+}