unittest: Disable MachineInstrClone.CopyCallSiteInfo on Windows

A bot error (http://45.33.8.238/win/12463/step_11.txt) reports 'unknown
file: error: SEH exception with code 0x3221225477 thrown in the test
body', but I don't know what causes this.

It looks like this has come up before, but afaict the root causes could
be different:

  https://reviews.llvm.org/rL329195, and in
  http://lists.llvm.org/pipermail/llvm-commits/Week-of-Mon-20180910/587425.html

I tried testing locally with UBSan, but that didn't uncover anything.