i too play war thunder but i'm not having problems with radeon mesa support. I'm using mesa 11.0.4 on a AMD A10 APU, on slackwre64-current (so it was recent packages) and also using the 4.1COMPAT flag. Please notice that i'm running the normal client, if you checked the "work-in-progress" flag on the laucher, you will get the new 64bit version of the game that AFAIK, still have problems/bugs.