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");
s</a><a class='active' href='/guix/log/etc/snippets/scheme-mode/guix-origin'>log</a><a href='/guix/tree/etc/snippets/scheme-mode/guix-origin?id=0eeaf1ac3cd5ea21cf126017b639efd964a759f5'>tree</a><a href='/guix/commit/etc/snippets/scheme-mode/guix-origin?id=0eeaf1ac3cd5ea21cf126017b639efd964a759f5'>commit</a><a href='/guix/diff/etc/snippets/scheme-mode/guix-origin?id=0eeaf1ac3cd5ea21cf126017b639efd964a759f5'>diff</a></td><td class='form'><form class='right' method='get' action='/guix/log/etc/snippets/scheme-mode/guix-origin'>
<input type='hidden' name='id' value='0eeaf1ac3cd5ea21cf126017b639efd964a759f5'/><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=0eeaf1ac3cd5ea21cf126017b639efd964a759f5'>root</a>/<a href='/guix/log/etc?id=0eeaf1ac3cd5ea21cf126017b639efd964a759f5'>etc</a>/<a href='/guix/log/etc/snippets?id=0eeaf1ac3cd5ea21cf126017b639efd964a759f5'>snippets</a>/<a href='/guix/log/etc/snippets/scheme-mode?id=0eeaf1ac3cd5ea21cf126017b639efd964a759f5'>scheme-mode</a>/<a href='/guix/log/etc/snippets/scheme-mode/guix-origin?id=0eeaf1ac3cd5ea21cf126017b639efd964a759f5'>guix-origin</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/snippets/scheme-mode/guix-origin?id=0eeaf1ac3cd5ea21cf126017b639efd964a759f5&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2019-05-09 00:22:37 -0400'>2019-05-09</span></td><td><a href='/guix/commit/etc/snippets/scheme-mode/guix-origin?id=4ac69ea10f54384ac893313ef738e5ad554ac328'>Add (guix bzr-download).</a><span class='msg-avail'>...<span class='msg-tooltip'>* guix/bzr-download.scm, guix/build/bzr.scm,
etc/snippets/scheme-mode/guix-bzr-reference: New files.
* Makefile.am (MODULES): Add them.
* etc/snippets/scheme-mode/guix-origin: Add "bzr-fetch" to the origin choices.
</span></span></td><td>Maxim Cournoyer</td></tr>