Add systemd system sleep hook dir

Enables the use and configuration of hooks in /etc/systemd/system-sleep. Which is used, for instance, by upower to notify the upower daemon of resume.
In order for NixOS to manage the system-sleep directory the systemd Makefile.am must be patched. Otherwise systemd will attempt to create and write to the directory directly during build. Which will fail. Since Makefile.am is patched the systemd build is extended to depend on automake and autoconf.
See the implementation of `services.udev.packages` in `udev.nix`:
```
      for i in ${toString cfg.packages}; do
        echo "Adding rules for package $i"
        for j in $i/{etc,lib}/udev/rules.d/*; do
          echo "Copying $j to $out/$(basename $j)"
          cat $j > $out/$(basename $j)
        done
      done
```
(I don't know why it's copying instead of symlinking here...)

It should also be possible to use `buildEnv` using the `pathsToLink` option, like
```
linkSleepHooks = buildEnv {
  paths = config.systemd.sleepHooks;
  pathsToLink = [ "/lib/systemd/system-sleep" ];
};
```