meson: re-add incorrect pkg-config files with GLVND for backward compatibility

Eric Engestrom requested to merge eric/mesa:glvnd-backward-compatible-fix into master

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

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)

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