In addition to adding the missing thread deps in the last commit, we
also appear to need to skip `-Wl,--as-needed` flags that Meson wants to
use, but doesn't work with our *BSD toolchains.
See https://github.com/mesonbuild/meson/issues/3593
They are not actually part of the store layer, but instead part of the
Nix executable infra (libraries don't need plugins, executables do).
This is part of a larger project of moving all of our legacy settings
infra to libmain, and having the underlying libraries just have plain
configuration structs detached from any settings infra / UI layer.
Progress on #5638
GitHub Actions seems to have magically switched architectures
without changing their identifiers.
See 2813ee66cb/README.md (available-images)
Maybe they have more complete documentation elsewhere, but it
seems to be incapable of selecting a runner based on architecture.
This avoids polluting nixComponents with things that aren't our
components.
Fixes the extraction of passthru tests, which failed for boehmgc
which had many irrelevant ones anyway.
