llvmpipe: Enable GLSL 450 for compat contexts too
829e9105 made the core and compat GLSL versions identical for softpipe, making it support 3.3 compat where llvmpipe had only 3.1, and we cannot allow the creation of a software renderer feature gap. This raises the compat version to 4.5 for llvmpipe.
Doesn't pass CI yet, trivially because I didn't update the expects yet, but also this turns a couple of tests from skip to fail, which I'd prefer to fix before merging.