Update Nixpkgs to use the updateAutotoolsGnuConfigScript hook everywhere
for Genode target platforms. Tweak Coreutils and Bash to compile, make
some tests.
Link with the libc and posix entrypoint library unless the -noposix flag
is passed. This allows the Genode Clang to be dropped into legacy build
systems.
Update the native packages using the Clang stdenv to pass -noposix.
Move the expansion of the Genode specific packages to the overlay as
nixpkgs.genodePackages and expose this as outputs.packages. This allows
access to offsets like buildPackages.genodePackages or
targetPackages.genodePackages.