i915: Do a test compile at glLinkShader() time.

i915: Do a test compile at glLinkShader() time.

This lets us throw errors back to the app for shaders that are too
complex.  The X server would really like to have this instead of guessing
based on renderer strings when shaders might be too complicated.

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/25533>