If GL3 isnt doable (CTG,ILK) expose the necesary bits to do GLSL 1.30 as EXT_gpu_shader4

[chrisforbes]

• Unsigned uniforms and attributes

[chrisforbes]

Turns out this is a horrid idea, and we'll do something called MESA_shading_language_130 instead, which will expose only the entrypoints.