[bug#49339] [PATCH core-updates] gnu: mesa: Update to 21.1.4.

[John Kehayias]

Hi everyone,

Final update, we still need the mesa-skip-tests.patch, but only for the i686 
part (second half). The other part of the patch is not needed as the test 
passes.

Here is the final version of the patch to just update Mesa to 21.1.4. Note this 
depends on the libdrm update of https://issues.guix.gnu.org/49412 Mesa builds 
as well as descendants I've tried (like xorg and friends).

Shall we get this merged and set the libglvnd updates after (in case we run 
into the core-updates freeze)? That would work well for me at least.

Thanks everyone,
John