Install systemd units in the right location

Debian uses /lib/systemd/system for system unit files, while i'm
putting ostree under the /usr prefix which means the hardcoded path
fails. Leave it to configure to work out the right location for systemd
units (method copied from pollkit).

Furthermore instead of installing the unit in local-fs.target.wants by
hand add a [Install] section so systemctl enable does the right thing

https://bugzilla.gnome.org/show_bug.cgi?id=705864

Makefile-dracut.am

@@ -23,13 +23,7 @@ dracutmoddir = $(prefix)/lib/dracut/modules.d/98ostree
 dracutmod_SCRIPTS = src/dracut/module-setup.sh
 dracutmod_DATA = src/dracut/ostree-prepare-root.service
 
-systemdunitdir = $(prefix)/lib/systemd/system
-systemdunit_DATA = src/dracut/ostree-remount.service
-
-INSTALL_DATA_HOOKS += install-remount-service-data-hook
-install-remount-service-data-hook:
-	mkdir -p $(DESTDIR)$(systemdunitdir)/local-fs.target.wants/
-	ln -s ../ostree-remount.service $(DESTDIR)$(systemdunitdir)/local-fs.target.wants/ostree-remount.service
+systemdsystemunit_DATA = src/dracut/ostree-remount.service
 
 dracutconfdir = $(sysconfdir)/dracut.conf.d
 dracutconf_DATA = src/dracut/ostree.conf

configure.ac

@@ -123,6 +123,16 @@ AC_ARG_WITH(dracut,
               [with_dracut=no])
 AM_CONDITIONAL(BUILDOPT_DRACUT, test x$with_dracut = xyes)
 
+AS_IF([test "x$with_dracut" = "xyes"], [
+  AC_ARG_WITH([systemdsystemunitdir],
+              AS_HELP_STRING([--with-systemdsystemunitdir=DIR], [Directory for systemd service files]),
+              [],
+              [with_systemdsystemunitdir=$($PKG_CONFIG --variable=systemdsystemunitdir systemd)])
+  AS_IF([test "x$with_systemdsystemunitdir" != "xno"], [
+    AC_SUBST([systemdsystemunitdir], [$with_systemdsystemunitdir])
+  ])
+])
+
 AC_CONFIG_FILES([
 Makefile
 embedded-dependencies/Makefile
@@ -140,5 +150,8 @@ echo "
     libsoup (retrieve remote HTTP repositories): $with_soup
     libarchive (parse tar files directly): $with_libarchive
     documentation: $enable_documentation
-    dracut: $with_dracut
-"
+    dracut: $with_dracut"
+if test "x$with_dracut" = "xyes" ; then
+    echo "    systemd unit dir: $with_systemdsystemunitdir"
+fi
+echo ""

src/dracut/ostree-remount.service

@@ -31,3 +31,6 @@ ExecStart=/usr/sbin/ostree-remount
 StandardInput=null
 StandardOutput=syslog
 StandardError=syslog+console
+
+[Install]
+WantedBy=local-fs.target