After the last stable update building mesa with codecs failed (…and mesa-nonfree is not up to date).
After some research I found this workaround and had success.
# https://bugs.archlinux.org/task/79821
# https://gitlab.freedesktop.org/mesa/mesa/-/issues/9908
sed -i 's/not have_mtls_dialect/false/' meson.build
It would be nice to include it, so others don’t have this mess.