continuation of #109595
pkgconfig was aliased in 2018, however, it remained in
all-packages.nix due to its wide usage. This cleans
up the remaining references to pkgs.pkgsconfig and
moves the entry to aliases.nix.
python3Packages.pkgconfig remained unchanged because
it's the canonical name of the upstream package
on pypi.
ee58a5b30d broke the plv8 build because it
upgraded the v8_6_x expression everywhere to the 6.9 branch, which came
with API changes. Notably, it seems plv8 only supports up-to v8 6.4.x at
this time.
This keeps a copy of the plv8_6_x expression inside the same directory
as the other v8 versions (so patches, etc are easy to apply), but it is
not exposed to the top-level of all-packages.nix.
Signed-off-by: Austin Seipp <aseipp@pobox.com>
