[MS] Don't emit coverage for deleting dtors

Summary:
The MS C++ ABI has no constructor variants, but it has destructor
variants, so we should move the deleting destructor variant check
outside the check for "does the ABI have constructor variants".

Fixes PR37561, so basic code coverage works on Windows with C++.

Reviewers: vsk

Subscribers: jdoerfert, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D58691

llvm-svn: 354924