glsl: Fail the build if the grammar contains shift/reduce errors.

When working on a parser, it's very easy to accidentally introduce
new shift/reduce conflicts.  Failing the build guarantees they'll
be noticed and fixed.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Chris Forbes <chrisf@ijw.co.nz>
1 file changed