Meson build

Created by: dcbaker

This series has grown a bit in scope from what I originally set out ot do, but I'm fiarly happy with the result. The idea is to use meson to build the mesa that we'll use for testing, and a lot of bugs got fixed along the way, especially for running on distros other than Debian.

I've tested this pretty extensively, and finally got m32 builds working correctly. I've got a final m64 build running on the mesa_custom branch right now, but this should be fine.

This also enables running most of the unit tests on the meson-buildtest instead of as part of the mesa passed to other projects, which should help relieve a bit more of the bottleneck in building mesa. There are a few tests that I need to write a meson patch for (or we can update to meson 0.44.0 and they'll just work). Each test is run individually, and the non gtests are wrapped by the build layer to produce JUnit xml.