[CUDA] Merge most of CodeGenCUDA/function-overload.cu into SemaCUDA/function-overload.cu.

Summary:
Previously we were using the codegen test to ensure that we choose the
right overload.  But we can do this within sema, with a bit of
cleverness.

I left the constructor/destructor checks in CodeGen, because these
overloads (particularly on the destructors) are hard to check in Sema.

Reviewers: tra

Subscribers: cfe-commits

Differential Revision: http://reviews.llvm.org/D18386

llvm-svn: 264207