When re-using a vtable slot for the nearest overridden method, just because

there's no return adjustment from the overridden to the overrider doesn't
mean there isn't a return adjustment from the overrider to the final
overrider.  This matters if we're emitting a virtual this-adjustment thunk
because the overrider virtually inherits from the class providing the
nearest overridden method.  Do the appropriate return adjustment in this case.

Fixes PR7611.

llvm-svn: 118466