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.
This is used in https://github.com/tweag/gomod2nix to reconstruct a
vendor metadata file.
With the vendor checks we need a lot more metadata which isn't
relevant for building packages, especially since we've already locked
the dependency graph ahead of time
This has been ported from FreeBSD: https://reviews.freebsd.org/D24122
The compiler does not need it anymore, has not needed it for many years
iirc. This just goes in and pollutes the environment overriding the
users GOPATH and causing grief.
Go even warns about it itself, without vs with this commit:
```sh
~> go env GOPATH
/home/manny/go
~> nix-shell -p go
~> go env GOPATH
warning: GOPATH set to GOROOT (/nix/store/gvw1mfpdrk7i82884yhxf9lf5j3c12zm-go-1.14.1/share/go) has no effect
/nix/store/gvw1mfpdrk7i82884yhxf9lf5j3c12zm-go-1.14.1/share/go
~> exit
~> nix-shell -I nixpkgs=cloned/NixOS/nixpkgs -p go
~> go env GOPATH
/home/manny/go
~> exit
```
