Required teaching lit.cfg.py to distinguish Windows the same way other projects do.
This should be system-windows. See config.py in llvm. By using system-windows, the test would be consistent with other platforms. Incidentally, I am just about to fix this as well as the test in LLVM that you changed to use windows - it should also use system-windows.
This really should live in config.py in llvm so that it can be used across all projects. And it should be system-windows for consistency with other platforms.