fix build to use default gcc toolchain which fixes link errors
associated with building against mismatched libstd++
patch vendored juice library to remove packed attributes which cause
compile errors but add static asserts to verify that the struct / class
layouts are identical regardless of attribute
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.
