Add $EUDEV_RULES_DIRECTORY to the list of rules directories.

The old udev 182 supported $UDEV_CONFIG_FILE, which in turn allowed
the search path to be customized, but eudev no longer has this, hence
this hack.

--- eudev-3.1.5/src/udev/udev-rules.c	2015-10-13 06:22:14.000000000 +0800
+++ eudev-3.1.5/src/udev/udev-rules.c	2015-10-16 20:45:38.491934336 +0800
@@ -47,15 +47,11 @@
         };
 };
 
-static const char* const rules_dirs[] = {
+static const char* rules_dirs[] = {
         UDEV_CONF_DIR "/rules.d",
         UDEV_RULES_DIR,
-        UDEV_ROOT_RUN "/udev/rules.d",
         UDEV_LIBEXEC_DIR "/rules.d",
-#ifdef HAVE_SPLIT_USR
-        "/lib/udev/rules.d",
-        "/usr/lib/udev/rules.d",
-#endif
+        NULL,			/* placeholder for $EUDEV_RULES_DIRECTORY */
         NULL};
 
 struct udev_rules {
@@ -1704,6 +1700,9 @@
 
         udev_rules_check_timestamp(rules);
 
+        /* Allow the user to specify an additional rules directory.  */
+        rules_dirs[3] = getenv("EUDEV_RULES_DIRECTORY");
+
         r = conf_files_list_strv(&files, ".rules", NULL, rules_dirs);
         if (r < 0) {
                 log_error_errno(r, "failed to enumerate rules files: %m");
f='/guix/refs/?id=d3adae38ca5df5644466f2ffd5cd23f4a514b06c'>refs</a><a class='active' href='/guix/log/etc/substitutes/berlin.guix.gnu.org.pub?showmsg=1'>log</a><a href='/guix/tree/etc/substitutes/berlin.guix.gnu.org.pub?id=d3adae38ca5df5644466f2ffd5cd23f4a514b06c'>tree</a><a href='/guix/commit/etc/substitutes/berlin.guix.gnu.org.pub?id=d3adae38ca5df5644466f2ffd5cd23f4a514b06c'>commit</a><a href='/guix/diff/etc/substitutes/berlin.guix.gnu.org.pub?id=d3adae38ca5df5644466f2ffd5cd23f4a514b06c'>diff</a></td><td class='form'><form class='right' method='get' action='/guix/log/etc/substitutes/berlin.guix.gnu.org.pub'>
<input type='hidden' name='id' value='d3adae38ca5df5644466f2ffd5cd23f4a514b06c'/><input type='hidden' name='showmsg' value='1'/><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=d3adae38ca5df5644466f2ffd5cd23f4a514b06c&amp;showmsg=1'>root</a>/<a href='/guix/log/etc?id=d3adae38ca5df5644466f2ffd5cd23f4a514b06c&amp;showmsg=1'>etc</a>/<a href='/guix/log/etc/substitutes?id=d3adae38ca5df5644466f2ffd5cd23f4a514b06c&amp;showmsg=1'>substitutes</a>/<a href='/guix/log/etc/substitutes/berlin.guix.gnu.org.pub?id=d3adae38ca5df5644466f2ffd5cd23f4a514b06c&amp;showmsg=1'>berlin.guix.gnu.org.pub</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/etc/substitutes/berlin.guix.gnu.org.pub?id=d3adae38ca5df5644466f2ffd5cd23f4a514b06c'>Collapse</a>)</th><th class='left'>Author</th></tr>
<tr class='logheader'><td><span title='2020-07-10 00:11:00 +0200'>2020-07-10</span></td><td class='logsubject'><a href='/guix/commit/etc/substitutes/berlin.guix.gnu.org.pub?id=d283bb960f927dd5f7bb8b96bc697221e4e8ad39'>maint: Remove traces of "berlin.guixsd.org".</a></td><td>Ludovic Courtès</td></tr>
<tr class='nohover-highlight'><td/><td colspan='3' class='logmsg'>
The guixsd.org domain is no longer advertised since before in 1.0.0
release in May 2019.

* etc/substitutes/berlin.guixsd.org.pub: Rename to...
* etc/substitutes/berlin.guix.gnu.org.pub: ... this.
* etc/substitutes/ci.guix.gnu.org.pub,
etc/substitutes/ci.guix.info.pub: Adjust accordingly.
* gnu/services/base.scm (%default-authorized-guix-keys): Likewise.
* guix/build/download-nar.scm (urls-for-item): Likewise.
* guix/self.scm (miscellaneous-files): Likewise.
* Makefile.am (dist_pkgdata_DATA): Likewise.


</td></tr>