Enable debug info tests on Windows

Now that new LLVM has landed, the debug info works on Windows as well.   Most existing tests pass, except for the following four, which I left disabled for now:
lexical-scope-in-for-loop
lexical-scope-in-if
lexical-scope-in-match
lexical-scopes-in-block-expression

Also, fixed a small problem with the debug info test runner.