[CUDA] Add additional testcases for EraseUnwantedCUDAMatches.

Summary:
Specifically, this patch adds testcases for all three calls to
EraseUnwantedCUDAMatches.  The addr-of-overloaded-fn test I accidentally
neutered in r264207, which moved much of
CodeGenCUDA/function-overload.cu into SemaCUDA/function-overload.cu.
The coverage from overloaded-delete test is new.

Reviewers: tra

Subscribers: cfe-commits

Differential Revision: http://reviews.llvm.org/D21913

llvm-svn: 275232