[Mesa-dev] ARB_shader_subroutine - first try

[Dave Airlie]

Hey,

This is my first submission of ARB_shader_subroutine, it's
been through a few internal revisions in my brain, and its based
on some parser work from Chris, but I may merge that stuff into
mine as I change his stuff heavily.

I implemented this by extending ir_call in the end and adding a lowering
pass to an if ladder.

The parser changes are a bit gnarly, but I tried to stay aligned
to the GLSL4.50 grammer which seems accurate for this.

Also I'm open on when to enable this, I really don't care about this
extension apart from the GL4.0 roadblock it has become.

Dave.