glsl: Add builtin variables for GLSL 3.00 ES.

glsl: Add builtin variables for GLSL 3.00 ES.

This patch also adds assertions so that when we add new GLSL versions,
we'll notice that we need to update the builtin variables.

[v2, idr]: s/Frab/Frag/  Noticed by Eric.

Reviewed-by: Ian Romanick <ian.d.romanick@intel.com> [v1]
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Eric Anholt <eric@anholt.net>
Acked-by: Carl Worth <cworth@cworth.org>