My previous attempts to bump the Darwin stdenv version didn't
seem to work, but AFAIK doing so should be straightforward
for anyone with a Darwin builder and the interest in tackling this.

While not the preferred solution, adding a conditional lets us move on,
as we missed 6 entirely due to no one getting around to resolving the
Darwin bootstrap accordingly.

This reverts commit 8505e71.

llvm uses response files in bootstrapping. It’s okay for them to
happen even though we don’t use expandResponseParams here right now.

* build w/iwd support since it's free (no dep required!)
* move to iputils for minor utilities, instead of inetutils
* parallel building :)

https://gitlab.freedesktop.org/NetworkManager/NetworkManager/raw/1.18.0/NEWS

https://github.com/ronf/asyncssh/blob/master/docs/changes.rst#release-1161-30-mar-2019

https://gitlab.gnome.org/GNOME/pygobject/blob/3.32.1/NEWS

https://pycairo.readthedocs.io/en/latest/changelog.html#v1-18-1

 python3Packages.pygobject3: 3.32.0 -> 3.32.1,  pythonPackages.pycairo: 1.18.0 -> 1.18.1

pythonPackages.asyncssh: 1.15.1 -> 1.16.1

Broken by the update in e03d551.

With 7.1 llvm-config looks for libLLVM-7.1.dylib, but the shortVersion
was still 7 so only 7 and 7.1.0 where aliased before.

	$ llvm-config --link-shared
	llvm-config: error: libLLVM-7.1.dylib is missing

Apply eb31e48 to older versions where applicable.