Driver: Produce crash diagnostics more often on Windows

Assertion failures call abort(), which return an exit code of 3 on
Windows.  The 'not' utility has the same check.

Unfortunately, the crash-report.c test requires a shell, so it does not
run for me locally, so I can only test this manually.

There's still more work to be done here: we should generate a batch
script instead of a shell script on Windows.

llvm-svn: 212481