meson: re-add incorrect pkg-config files with GLVND for backward compatibility
This is a bit counter-intuitive, but the issue is that GLVND is broken in versions <= 1.1.1, so we need to keep wrongly providing these files to cover up their mistake, otherwise the rest of the world ends up broken.
Suggested-by: @dbaker
Cc: mesa-stable@lists.freedesktop.org
Note: adding this MR to the %19.2 Release Tracker not because it should block it but to track that it should be cherry-picked to it (although landing before 19.2.0 comes out would be best for user/packager experience)