glsl: Add compute shader builtin variables for OpenGLES 3.1
glsl: Add compute shader builtin variables for OpenGLES 3.1

Signed-off-by: Jordan Justen <a79006884ba9cf5f4f7fcbb92a15b208780d8c97@intel.com>
Reviewed-by: Iago Toral Quiroga <a847aabaac44184372f6b1cd1a59aa254daaeb0b@igalia.com>
Reviewed-by: Marta Lofstedt <d284b1e5d144aa8ffd9d3937a966cb84599af26e@intel.com>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler