glsl: Parse 0 as a preprocessor INTCONSTANT

glsl: Parse 0 as a preprocessor INTCONSTANT

This allows a more reasonable error message for '#version 0' of

    0:1(10): error: GLSL 0.00 is not supported. Supported versions are: 1.10, 1.20, 1.30, 1.00 ES, 3.00 ES, 3.10 ES, and 3.20 ES

instead of

    0:1(10): error: syntax error, unexpected $undefined, expecting INTCONSTANT

Signed-off-by: Ian Romanick <ian.d.romanick@intel.com>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=97420
Reviewed-by: Nicolai Hähnle <nicolai.haehnle@amd.com>
Cc: mesa-stable@lists.freedesktop.org
Cc: Juan A. Suarez Romero <jasuarez@igalia.com>
Cc: Karol Herbst <karolherbst@gmail.com>