While I cannot get portage to compile llvm from git (neither from master, nor
from your branch) without getting an error
(https://forums.gentoo.org/viewtopic-t-1013718.html), I've tried to apply the
commits "R600/SI: Disable register pressure tracking in the scheduler"
(11a8738d716fa9f67da9fce2892c30352780e89b) and "XXX: Schedmodul"
(b08f2e3be487f399b04363972bfd5dfc05652673) to llvm-3.6. 
The patches apply and the resulting code compiles and installs fine, but the
game still crashes at the same spot.