Compare canonical return types when generating MS C++ ABI vtable thunks

This was part of the cause for PR17655.  We were generating thunks when
we shouldn't have.  I suspect that if we tweak the test case for PR17655
to actually require thunks, we can reproduce the same crash.

llvm-svn: 197836
diff --git a/clang/lib/AST/VTableBuilder.cpp b/clang/lib/AST/VTableBuilder.cpp
index 5f7ae0f..63ac6f2 100644
--- a/clang/lib/AST/VTableBuilder.cpp
+++ b/clang/lib/AST/VTableBuilder.cpp
@@ -2888,7 +2888,8 @@
         AddThunk(MD, VTableThunks[OverriddenMethodInfo.VFTableIndex]);
       }
 
-      if (MD->getResultType() == OverriddenMD->getResultType()) {
+      if (Context.hasSameType(MD->getResultType(),
+                              OverriddenMD->getResultType())) {
         // No return adjustment needed - just replace the overridden method info
         // with the current info.
         MethodInfo MI(OverriddenMethodInfo.VBTableIndex,