xfbuild crashes OPTLINK on Windows if +o has forward slashes
If you invoke xfbuild with an +oPATH argument where the PATH contains forward slashes, OPTLINK explodes.
This is actually because dmd is too stupid to actually sanitise what it passes to OPTLINK. It'd be really nice if xfbuild did the necessary directory separator normalisation.
Tested with latest trunk xfbuild and dmd 1.051.