[glsl-in] Doesn't support commas in structure definitions

[Jasper St. Pierre]

I have a structure like this:

struct LightScatteringParams {
    float BetaRay, BetaMie, HGg, DistanceMul, BlendCoeff;
    vec3 SunDirection, SunColor;
};

It is relatively easy to reformat it to support naga, but naga should support this.