gitlab-ci: merge meson-glvnd into meson-swr

gitlab-ci: merge meson-glvnd into meson-swr

There's no need to have a whole build just for that flag, we can add it
to any build.

v2: Add a note about why we put glvnd where we did (by anholt).

Signed-off-by: Eric Engestrom <eric.engestrom@intel.com>
Reviewed-by: Eric Anholt <eric@anholt.net>
Reviewed-by: Michel Dänzer <michel.daenzer@amd.com>
Reviewed-by: Eric Engestrom <eric.engestrom@intel.com> (v2)
Acked-by: Dylan Baker <dylan@pnwbakers.com>