[Sema] Fix assertion hit with #pragma weak.

rdar://16264844

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@203372 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Sema/SemaDeclAttr.cpp

@@ -4655,6 +4655,8 @@ void Sema::DeclApplyPragmaWeak(Scope *S, NamedDecl *ND, WeakInfo &W) {
     // to insert Decl at TU scope, sorry.
     DeclContext *SavedContext = CurContext;
     CurContext = Context.getTranslationUnitDecl();
+    NewD->setDeclContext(CurContext);
+    NewD->setLexicalDeclContext(CurContext);
     PushOnScopeChains(NewD, S);
     CurContext = SavedContext;
   } else { // just add weak to existing

test/SemaCXX/pragma-weak.cpp

@@ -6,3 +6,6 @@ extern "C" {
   void foo() {
   };
 }
+
+extern "C" int Test;
+#pragma weak test = Test