[modules] Don't save uninteresting identifiers, and don't consider identifiers
to be interesting just because they are the name of a builtin. Reduces the size
of an empty module by over 80% (~100KB).

llvm-svn: 242650
diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index 2bf7356..042cffc 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -3115,7 +3115,7 @@
       // remain visible, a single bogus local redeclaration (which is
       // actually only a warning) could break all the downstream code.
       if (!New->getLexicalDeclContext()->isFunctionOrMethod())
-        New->getIdentifier()->setBuiltinID(Builtin::NotBuiltin);
+        New->getIdentifier()->revertBuiltin();
 
       return false;
     }