Improve the const-ness of a few methods.
No functionality change.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@57417 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/AST/DeclCXX.cpp b/lib/AST/DeclCXX.cpp
index 0a65ab3..3f93791 100644
--- a/lib/AST/DeclCXX.cpp
+++ b/lib/AST/DeclCXX.cpp
@@ -54,7 +54,8 @@
 
 QualType CXXMethodDecl::getThisType(ASTContext &C) const {
   assert(isInstance() && "No 'this' for static methods!");
-  QualType ClassTy = C.getTagDeclType(cast<CXXRecordDecl>(getParent()));
+  QualType ClassTy = C.getTagDeclType(const_cast<CXXRecordDecl*>(
+                                            cast<CXXRecordDecl>(getParent())));
   QualType ThisTy = C.getPointerType(ClassTy);
   ThisTy.addConst();
   return ThisTy;