[TypeChecker] Disable use of using in macro extensions

Author: xedin

lib/Sema/TypeCheckMacros.cpp

@@ -603,7 +603,8 @@ static void diagnoseInvalidDecl(Decl *decl,
       isa<OperatorDecl>(decl) ||
       isa<PrecedenceGroupDecl>(decl) ||
       isa<MacroDecl>(decl) ||
-      isa<ExtensionDecl>(decl)) {
+      isa<ExtensionDecl>(decl) ||
+      isa<UsingDecl>(decl)) {
     decl->diagnose(diag::invalid_decl_in_macro_expansion, decl);
     decl->setInvalid();