Comment 15 for bug 1039155

As I see it, there are three situations we need to care about here:

1) There's no hardware 3D support at all. In this case llvmpipe *will* kick in automatically; see @Colin's unity-support-test output. In this case there's no need to set LIBGL_ALWAYS_SOFTWARE

2) There *is* 3D hardware support provided by mesa, but it's insufficient to run Unity. In this case, we *do* need to force software with LIBGL_ALWAYS_SOFTWARE=1. Setting that in the global environment is a bit hostile, though; they may have enough 3D support for other programs, and this will disable it.

3) The user has a non-mesa 3D stack enabled, and it doesn't provide enough 3D for Unity. In this case there's pretty much nothing we can do. Non-mesa 3D stacks replace libGL, so we can't load llvmpipe, and even if we tried LD_LIBRARY_PATH hacks to get mesa's libGL, non-mesa 3D stacks generally also replace X server components with incompatible versions.