ci: gentoo: make vala tests actually run

Gentoo does a weirdo thing where you cannot detect vala without setting
an environment variable. It's usually only set in ebuild recipes, and
vala simply does not work on Gentoo at all, period, end of story,
outside of that.

Capitulate, and parse the output of portage to find the most recent vala
installed and export that directly into meson's binary table lookup. We
aren't interested in whether *Gentoo* works with Vala, we are interested
in finding out whether newly packaged vala versions in Gentoo are
compatible with meson.

Bug: https://bugs.gentoo.org/513658

0 files changed, 0 insertions, 0 deletions