glsl: don't run the GLSL pre-processor when we are skipping compilation

glsl: don't run the GLSL pre-processor when we are skipping compilation

This moves the hashing of shader source for the cache lookup to before
the preprocessor.  In our experience, shaders are unlikely to hash the
same after preprocessing if they didn't hash the same before, so we can
skip preprocessing for cache hits.

Improves Deus Ex start-up times with a warm cache from ~30 seconds to
~22 seconds.

Also fixes the leaking of state.

V2: fix indentation

v3: add the value of MESA_EXTENSION_OVERRIDE to the hash of the shader.

Tested-by (v2): Grazvydas Ignotas <notasas@gmail.com>
Tested-by: Dieter Nützel <Dieter@nuetzel-hh.de>
Reviewed-by: Eric Anholt <eric@anholt.net>