Allow a using directive to refer to the implicitly-defined namespace
"std", with a warning, to improve GCC compatibility. Fixes PR7517.

As a drive-by, add typo correction for using directives.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@107172 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Sema/Sema.h b/lib/Sema/Sema.h
index fcf5e94..325add7 100644
--- a/lib/Sema/Sema.h
+++ b/lib/Sema/Sema.h
@@ -2120,6 +2120,7 @@
                                            AttributeList *AttrList);
   virtual void ActOnFinishNamespaceDef(DeclPtrTy Dcl, SourceLocation RBrace);
 
+  NamespaceDecl *getStdNamespace();
   virtual DeclPtrTy ActOnUsingDirective(Scope *CurScope,
                                         SourceLocation UsingLoc,
                                         SourceLocation NamespcLoc,