glsl: Convert the tests directory to automake.

glsl: Convert the tests directory to automake.

This runs optimization-test and produces the usual automake test
output, which may be interesting to automated build systems.

This doesn't convert the tests to be individually exposed to the
automake runner, because automake doesn't like wildcards (due to being
nonportable in make, not that we care).

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>