http://bugs.winehq.org/show_bug.cgi?id=27145
--- Comment #52 from Stefan Dösinger stefan@codeweavers.com 2011-12-20 03:16:46 CST --- It's possible that the game works on Intel GPUs, especially if you have an up-to-date kernel and Mesa version. Otherwise, bug 27264 seems to be exactly the same issue, and the game appears to be less demanding, especially in the main menu where the bug occurs.
It might be a hack like that, but I have my doubts. The weapon would be properly clipped, but not depth-tested. It is possible that they don't need depth testing for the weapon at all(e.g. proper draw order, or culling being enough for hidden surface removal), but it that case they could just disable the depth test and get the same result.