[CUDA] Don't assume that destructors can't be overloaded.

Summary:
You can overload a destructor in CUDA, and SemaOverload needs to be
tweaked not to crash when it sees an explicit call to an overloaded
destructor.

Reviewers: rsmith

Subscribers: cfe-commits, tra

Differential Revision: http://reviews.llvm.org/D21912

llvm-svn: 275231