From https://github.com/Hummer12007/brightnessctl/issues/67

--- a/Makefile
+++ b/Makefile
@@ -18,6 +18,8 @@ MODE = ${MODE_${INSTALL_UDEV_RULES}}
 ifdef ENABLE_SYSTEMD
 	CFLAGS += ${shell pkg-config --cflags libsystemd}
 	LDLIBS += ${shell pkg-config --libs libsystemd}
+	CFLAGS += ${shell pkg-config --cflags libelogind}
+	LDLIBS += ${shell pkg-config --libs libelogind}
 	CPPFLAGS += -DENABLE_SYSTEMD
 	INSTALL_UDEV_RULES=0
 	MODE = 0755
png' alt='cgit logo'/></a></td>
<td class='main'><a href='/'>index</a> : <a href='/guix/'>guix</a></td><td class='form'><form method='get'>
<input type='hidden' name='id' value='1463e9504b116ea0874a0643a6dd23c957f3e506'/><select name='h' onchange='this.form.submit();'>
<option value='koszko' selected='selected'>koszko</option>
<option value='koszko-scripts'>koszko-scripts</option>
</select> <input type='submit' value='switch'/></form></td></tr>
<tr><td class='sub'>Wojtek's customized Guix</td><td class='sub right'></td></tr></table>
<table class='tabs'><tr><td>
<a href='/guix/about/'>about</a><a href='/guix/'>summary</a><a href='/guix/refs/?id=1463e9504b116ea0874a0643a6dd23c957f3e506'>refs</a><a class='active' href='/guix/log/gnu/packages/acl.scm'>log</a><a href='/guix/tree/gnu/packages/acl.scm?id=1463e9504b116ea0874a0643a6dd23c957f3e506'>tree</a><a href='/guix/commit/gnu/packages/acl.scm?id=1463e9504b116ea0874a0643a6dd23c957f3e506'>commit</a><a href='/guix/diff/gnu/packages/acl.scm?id=1463e9504b116ea0874a0643a6dd23c957f3e506'>diff</a></td><td class='form'><form class='right' method='get' action='/guix/log/gnu/packages/acl.scm'>
<input type='hidden' name='id' value='1463e9504b116ea0874a0643a6dd23c957f3e506'/><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=1463e9504b116ea0874a0643a6dd23c957f3e506'>root</a>/<a href='/guix/log/gnu?id=1463e9504b116ea0874a0643a6dd23c957f3e506'>gnu</a>/<a href='/guix/log/gnu/packages?id=1463e9504b116ea0874a0643a6dd23c957f3e506'>packages</a>/<a href='/guix/log/gnu/packages/acl.scm?id=1463e9504b116ea0874a0643a6dd23c957f3e506'>acl.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/gnu/packages/acl.scm?id=1463e9504b116ea0874a0643a6dd23c957f3e506&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2020-10-27 12:02:31 +0100'>2020-10-27</span></td><td><a href='/guix/commit/gnu/packages/acl.scm?id=559c134b0ece171fcd39b31e5444b955deefcc8e'>gnu: acl: Fix cross-compilation.</a><span class='msg-avail'>...</span></td><td>Mathieu Othacehe</td></tr>
<tr><td><span title='2020-10-10 18:21:08 +0200'>2020-10-10</span></td><td><a href='/guix/commit/gnu/packages/acl.scm?id=6693eac6eb9e13852f2b4156f1e9ebcd70ec43b6'>gnu: acl: Disable tests for the Hurd.</a><span class='msg-avail'>...</span></td><td>Jan (janneke) Nieuwenhuizen</td></tr>
<tr><td><span title='2020-01-14 18:31:36 +0100'>2020-01-14</span></td><td><a href='/guix/commit/gnu/packages/acl.scm?id=ecfe153706b62714c9d0c2af347fca6e84f6f28a'>gnu: acl: Do not build the static library.</a><span class='msg-avail'>...</span></td><td>Marius Bakke</td></tr>