[Mesa-dev] Testing out Kristian's fast mtx patch

[Timothy Arceri]

After a recent discussion about this code from 2015 I was curious
to give it a try. The outstanding review item was that we shouldn't
be replacing the C11 mtx type/functions with our own, so I've renamed
the fast path to simple_mtx* and added a couple of patches to make use
of it.

The idea is this fast mtx can be used in place of the full mtx 
implementation when its of type mtx_plain.

I though if anywhere we might see a change in the drawoverhead piglit
test but I didn't see any real change.

Anyway since I've made the updates I thought I'd send it out. Maybe
someone else might find some better results. Kristian reported a 10%
increase in some internal Intel benchmarks, I wonder if thats still the
case.