On Windows, we now use RaiseException to generate the kind of trap we require (one...

On Windows, we now use RaiseException to generate the kind of trap we require (one which calls our vectored exception handler), and fall back to using a volatile write to simulate a trap elsewhere.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@228628 91177308-0d34-0410-b5e6-96231b3b80d8