Hey Guix,

this patch series changes libdrm and Mesa to use Meson.

A few notes to go along with the patches:

Patch #1: Libdrm on Github mentions that Autotools is the legacy build
system for libdrm, so it seems better to change this to use Meson.
Patch #2: Mesa is gonna drop support for Autotools entirely at some
point in 2019, so it seems good to make the switch sooner rather than
later. I think I converted all the configure flags to the new format.
Patches #3-6: For some reason these packages now need an explicit mesa
input. I haven't run into other packages that have this problem yet.