[Mesa-dev] gallium includes from Mesa, nir.h stops using Mesa main.

[Eric Anholt]

OK, I think this is kind of the next step from the gallium-versus-mesa
includes discussion earlier: Accept that u_math.h is an OK name, and the
parent directory is OK, too, and just start sharing code.  Once that's in
place, I can get bitset.h out of Mesa main and into util/, so that nir.h
doesn't use any of Mesa main (and we can use it from gallium drivers, too
-- freedreno seems to want it, and I've wanted to use it in vc4).

I still have mtypes.h dependencies in my TGSI-to-NIR code, because I'm
using its interpolation qualifier definitions (and should be using the
VARYING defines, too).  That will be a thing to do something sensible
about if this can land in the first place.