bug#43849: mesa is not reproducible

[zimoun]

Dear Danny,

You asked on guix-devel since when Mesa is not reproducible: at least
since v1.1.0.

  git --no-pager log v1.1.0 -1 --format='%H'
  d62c9b2671be55ae0305bebfda17b595f33797f2

  guix time-machine --commit=d62c9b2671be55ae0305bebfda17b595f33797f2 \
       -- build mesa
  guix time-machine --commit=d62c9b2671be55ae0305bebfda17b595f33797f2 \
       -- build mesa --no-grafts --check -K

--8<---------------cut here---------------start------------->8---
guix build: error: derivation 
`/gnu/store/wsp9wf83bbsmz8x061rhqndx05zmjff0-mesa-19.3.4.drv' may not be 
deterministic: output `/gnu/store/2mf0clz9w64diy0kz11qcs4q5wg9hc6z-mesa-19.3.4' 
differs from ?/gnu/store/2mf0clz9w64diy0kz11qcs4q5wg9hc6z-mesa-19.3.4-check?
--8<---------------cut here---------------end--------------->8---

And the differing files are:

 - lib/dri/iris_dri.so
 - lib/dri/nouveau_drv_video.so
 - lib/libvulkan_radeon.so
 - lib/vdpau/libvdpau_nouveau.so.1.0.0


All the best,
simon