systemd: Separate lib output

This moves libsystemd.so and libudev.so into systemd.lib, and gets rid
of libudev (which just contained a copy of libudev.so and the udev
headers). It thus reduces the closure size of all packages that
(indirectly) depend on libsystemd, of which there are quite a few (for
instance, PulseAudio and dbus). For example, it reduces the closure of
Blender from 430.8 to 400.8 MiB.

pkgs/development/libraries/mesa/default.nix

@@ -1,6 +1,6 @@
 { stdenv, fetchurl, fetchpatch
 , pkgconfig, intltool, autoreconfHook, substituteAll
-, file, expat, libdrm, xorg, wayland, libudev
+, file, expat, libdrm, xorg, wayland, systemd
 , llvmPackages, libffi, libomxil-bellagio, libva
 , libelf, libvdpau, python
 , grsecEnabled ? false
@@ -54,7 +54,7 @@ stdenv.mkDerivation {
   ] ++ optional stdenv.isLinux
       (substituteAll {
         src = ./dlopen-absolute-paths.diff;
-        libudev = libudev.out;
+        libudev = systemd.lib;
       });
 
   postPatch = ''
@@ -114,7 +114,7 @@ stdenv.mkDerivation {
     libffi wayland libvdpau libelf libXvMC
     libomxil-bellagio libva libpthreadstubs
     (python.withPackages (ps: [ ps.Mako ]))
-  ] ++ optional stdenv.isLinux libudev;
+  ] ++ optional stdenv.isLinux systemd;
 
 
   enableParallelBuilding = true;