New meson build system

This is a completely new, from scratch, pass at a meson build system for libglvnd. It uses a new version of meson and takes advantage of many of the nice features to be added in that time. I think I could remove the use of these features if getting back to the same version as mesa is important (mesa requires 0.46, this requires so 0.48, 0.52 is current).

From a performance point of view this speaks for itself, meson+ninja is ~4x faster than autoget+configure+make without ccache, and ~3x faster than autogen+configure+make with ccache. From a community point of view meson is quickly becoming the de factor build system of freedesktop projects: libdrm and mesa have already dropped autotools support, xorg has meson and will eventually drop autotools. Meson offers a lot of maintainability improvements, as it's scripting language is a OOO by design rather than side-effect by design.

All of the unit-test pass, and I've run this with mesa (i965) through the piglit sanity profile.