Make the non-const DeclContext::getParent call the const version, instead of the other way around.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@59646 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/include/clang/AST/DeclBase.h b/include/clang/AST/DeclBase.h
index ba94807..bfc7607 100644
--- a/include/clang/AST/DeclBase.h
+++ b/include/clang/AST/DeclBase.h
@@ -294,9 +294,10 @@
 public:
   /// getParent - Returns the containing DeclContext if this is a ScopedDecl,
   /// else returns NULL.
-  DeclContext *getParent();
-  const DeclContext *getParent() const {
-    return const_cast<DeclContext*>(this)->getParent();
+  const DeclContext *getParent() const;
+  DeclContext *getParent() {
+    return const_cast<DeclContext*>(
+                             const_cast<const DeclContext*>(this)->getParent());
   }
 
   bool isFunctionOrMethod() const {