[Nix-dev] libdrm&mesa upgrade

[Peter Simons]

Hi Yury,

 > The attached patch upgrades libdrm and mesa to the latest versions.

I have tested the updated versions, and they work fine. In fact, the
update greatly improved the stability of hardware accelerated OpenGL
rendering on my machine, i.e. several crashes that I used to see
regularly in Asymptote are now gone.

I am very much in favor of committing those updates to trunk.

Take care,
Peter