[CFI] Disable CFI checks for __cxa_decrement_exception_refcount

Summary:
exception_header->exceptionDestructor is a void(*)(void*) function
pointer; however, it can point to destructors like std::
exception::~exception that don't match that type signature.

Reviewers: pcc, vitalybuka

Reviewed By: vitalybuka

Subscribers: kcc, christof, cfe-commits

Differential Revision: https://reviews.llvm.org/D45455

llvm-svn: 329629