I'm not familiar with Manjaro Linux, but usually there is a package with a -dbg
or similar suffix, e.g. mesa-dbg, llvm-dbg, something like that.

And yes, it's not surprising that the r300 driver crashes later because it
doesn't usually use LLVM. My guess is that Awesomenauts hits a path where some
of the software paths for vertex shading are used and then it crashes.