i965: Dump linked shaders on MESA_GLSL=dump.

i965: Dump linked shaders on MESA_GLSL=dump.

Often, the original shader IR isn't terribly interesting because a lot
of crucial optimizations haven't been done (such as inlining built-ins).

ir_to_mesa used to print this out for us, but since we don't use it, we
have to do it ourselves.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Eric Anholt <eric@anholt.net>