vrend: Fix issues with host compatibility profile and make it possible to force a compatibility context on the host
- Rework the use of the GLSL version, prefer GLSL level >= 140 on the host when available
- Fix some places where we didn't set the requirement correctly
- Prefer handling clip planes, polygon stipple, flat shading, and two-side colors in shader when run on GL 3.1+
- Signal guest to lower primitives and color clamping also on compat profile host
- Add option to request a compatibility profile and add an according flag to vtest
With that I found no piglit regressions when using a GL 4.6 compatibility profile instead of a core profile, and a number of test are fixed.
CI needs changes to the mesa CI setup, because we re-use their scripts to run virgl_test_server, so after landing this we can add a run to the mesa-CI and then add it here.
Edited by Gert Wollny