[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

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@275231 91177308-0d34-0410-b5e6-96231b3b80d8