[Mesa-dev] Hardware agnostic on-disk shader cache patches

[Timothy Arceri]

The refactoring series is now pushed so here is the hardware agnostic
shader cache patches.

In future I want to change the way we track Mesa versions in patch 24
by creating a new cache directory for each Mesa version. This will
help avoid unnecessary fallback recompiles and also allow 3rd parties
to easily distribute precompiled shaders. However for now patch 24
works fine and I'd rather not hold up this series any longer.