glsl: Set new GLSL 1.50 constants correctly.

This patch populates the following built-in GLSL 1.50 variables based
on constants stored in ctx->Const:

- gl_MaxVertexOutputComponents
- gl_MaxGeometryInputComponents
- gl_MaxGeometryOutputComponents
- gl_MaxFragmentInputComponents
- gl_MaxGeometryTextureImageUnits
- gl_MaxGeometryOutputVertices
- gl_MaxGeometryTotalOutputComponents
- gl_MaxGeometryUniformComponents
- gl_MaxGeometryVaryingComponents

On i965/gen7, fixes all Piglit tests in "spec/glsl-1.50/built-in
constants/*" except for gl_MaxCombinedTextureImageUnits and
gl_MaxGeometryUniformComponents.