libiomp doesn't build on Windows after r273599

r273599 added the -DUNICODE build flag, breaking the libiomp build.

I've worked around it in r273898 to unblock this week's Windows
snapshot, but it would be great if someone could take a proper look.

It would be even better if there were buildbots that could catch these
issues automatically, before I run into them trying to build the
weekly snapshots :slight_smile:


We are looking at it now! Thanks for letting us know.

-- Johnny