[Piglit] [RFC] unify builtin_function based tests.

[Dylan Baker]

This series is the last (and original) bits of my reworking of the test
generator code in piglit. This series gets most of the way toward
unifying builtin_uniform and builtin_uniform_fp64 into a single
generator.

This series achieves that goal by first splitting code that is exactly
duplicated between the fp64 and non-fp64 module into separate modules,
then sharing these new split modules. Then it converts the non-fp64
generator to mako. Finally it merges the fp64 version into the non-fp64
version.

The second to last patch enables CS tests on fp64, and the final patch
makes Jordan's recent patch work on top of these changes.

This series is marked RFC because I cannot get a system with
ARB_gpu_shader_fp64 running, so I can't actually test this. They
generate successfully and using diff I believe that there are only
whitespace changes remaining, but since I can't test I can't be sure.

This is available at my github:
https://github.com/dcbaker/piglit submit/generated-mako