Don't install systemd units unless using libsystemd session tracking.

Submitted upstream:

  https://gitlab.freedesktop.org/polkit/polkit/-/merge_requests/134

diff --git a/data/meson.build b/data/meson.build
--- a/data/meson.build
+++ b/data/meson.build
@@ -26,7 +26,7 @@ if enable_pam
   )
 endif
 
-if enable_logind
+if session_tracking == 'libsystemd-login'
   configure_file(
     input: 'polkit.service.in',
     output: '@BASENAME@',
diff --git a/meson.build b/meson.build
--- a/meson.build
+++ b/meson.build
@@ -199,7 +199,7 @@ if enable_logind
 
   # systemd unit / service files
   systemd_systemdsystemunitdir = get_option('systemdsystemunitdir')
-  if systemd_systemdsystemunitdir == ''
+  if systemd_systemdsystemunitdir == '' and session_tracking == 'libsystemd-login'
     systemd_dep = dependency('systemd', not_found_message: 'systemd required but not found, please provide a valid systemd user unit dir or disable it')
     # FIXME: systemd.pc file does not use variables with relative paths, so `define_variable` cannot be used
     systemd_systemdsystemunitdir = systemd_dep.get_pkgconfig_variable('systemdsystemunitdir')
'>refs</a><a class='active' href='/guix/log/tests/processes.scm'>log</a><a href='/guix/tree/tests/processes.scm?id=b67013c8ca28c5f5b5c5e1eeb869870c2c1dabe9'>tree</a><a href='/guix/commit/tests/processes.scm?id=b67013c8ca28c5f5b5c5e1eeb869870c2c1dabe9'>commit</a><a href='/guix/diff/tests/processes.scm?id=b67013c8ca28c5f5b5c5e1eeb869870c2c1dabe9'>diff</a></td><td class='form'><form class='right' method='get' action='/guix/log/tests/processes.scm'>
<input type='hidden' name='id' value='b67013c8ca28c5f5b5c5e1eeb869870c2c1dabe9'/><select name='qt'>
<option value='grep'>log msg</option>
<option value='author'>author</option>
<option value='committer'>committer</option>
<option value='range'>range</option>
</select>
<input class='txt' type='search' size='10' name='q' value=''/>
<input type='submit' value='search'/>
</form>
</td></tr></table>
<div class='path'>path: <a href='/guix/log/?id=b67013c8ca28c5f5b5c5e1eeb869870c2c1dabe9'>root</a>/<a href='/guix/log/tests?id=b67013c8ca28c5f5b5c5e1eeb869870c2c1dabe9'>tests</a>/<a href='/guix/log/tests/processes.scm?id=b67013c8ca28c5f5b5c5e1eeb869870c2c1dabe9'>processes.scm</a></div><div class='content'><table class='list nowrap'><tr class='nohover'><th class='left'>Age</th><th class='left'>Commit message (<a href='/guix/log/tests/processes.scm?id=b67013c8ca28c5f5b5c5e1eeb869870c2c1dabe9&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2019-12-10 10:49:42 +0100'>2019-12-10</span></td><td><a href='/guix/commit/tests/processes.scm?id=0b5ad0e756a34d5e3ed1f37c3d4083a330fa33f5'>tests: processes: Skip tests if running with binfmt.</a><span class='msg-avail'>...<span class='msg-tooltip'>* tests/processes.scm (binfmt-misc?): New procedure,
(test-assert*): new procedure that skips the test if binfmt-misc? returns
</span></span></td><td>Mathieu Othacehe</td></tr>
<tr><td><span title='2018-10-29 00:13:38 +0100'>2018-10-29</span></td><td><a href='/guix/commit/tests/processes.scm?id=63eb2b899be7ac857454442e09d0ebd23fe4f871'>Add 'guix processes'.</a><span class='msg-avail'>...<span class='msg-tooltip'>* guix/scripts/processes.scm, tests/processes.scm: New files.
* Makefile.am (MODULES): Add the former.
(SCM_TESTS): Add the latter.
* po/guix/POTFILES.in: Add guix/scripts/processes.scm.
* doc/guix.texi (Invoking guix processes): New node.
(Invoking guix-daemon): Reference it.
</span></span></td><td>Ludovic Courtès</td></tr>