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");
e' href='/guix/log/gnu/build/linux-initrd.scm'>log</a><a href='/guix/tree/gnu/build/linux-initrd.scm?id=0be51fe03bf2b8f3ef009929fa0860e17aa15de4'>tree</a><a href='/guix/commit/gnu/build/linux-initrd.scm?id=0be51fe03bf2b8f3ef009929fa0860e17aa15de4'>commit</a><a href='/guix/diff/gnu/build/linux-initrd.scm?id=0be51fe03bf2b8f3ef009929fa0860e17aa15de4'>diff</a></td><td class='form'><form class='right' method='get' action='/guix/log/gnu/build/linux-initrd.scm'>
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<div class='path'>path: <a href='/guix/log/?id=0be51fe03bf2b8f3ef009929fa0860e17aa15de4'>root</a>/<a href='/guix/log/gnu?id=0be51fe03bf2b8f3ef009929fa0860e17aa15de4'>gnu</a>/<a href='/guix/log/gnu/build?id=0be51fe03bf2b8f3ef009929fa0860e17aa15de4'>build</a>/<a href='/guix/log/gnu/build/linux-initrd.scm?id=0be51fe03bf2b8f3ef009929fa0860e17aa15de4'>linux-initrd.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/build/linux-initrd.scm?id=0be51fe03bf2b8f3ef009929fa0860e17aa15de4&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2020-12-15 17:32:10 +0100'>2020-12-15</span></td><td><a href='/guix/commit/gnu/build/linux-initrd.scm?id=6a060ff27ff68384d7c90076baa36c349fff689d'>store-copy: 'populate-store' can optionally deduplicate files.</a><span class='msg-avail'>...<span class='msg-tooltip'>Until now deduplication was performed as an additional pass after
copying files, which involve re-traversing all the files that had just
been copied.

* guix/store/deduplication.scm (copy-file/deduplicate): New procedure.
* tests/store-deduplication.scm ("copy-file/deduplicate"): New test.
* guix/build/store-copy.scm (populate-store): Add #:deduplicate?
parameter and honor it.
* tests/gexp.scm ("gexp-&gt;derivation, store copy"): Pass #:deduplicate? #f
to 'populate-store'.
* gnu/build/image.scm (initialize-root-partition): Pass #:deduplicate?
to 'populate-store'.  Pass #:deduplicate? #f to 'register-closure'.
* gnu/build/vm.scm (root-partition-initializer): Likewise.
* gnu/build/install.scm (populate-single-profile-directory): Pass
 #:deduplicate? #f to 'populate-store'.
* gnu/build/linux-initrd.scm (build-initrd): Likewise.
* guix/scripts/pack.scm (self-contained-tarball)[import-module?]: New
procedure.
[build]: Pass it as an argument to 'source-module-closure'.
* guix/scripts/pack.scm (squashfs-image)[build]: Wrap in
'with-extensions'.
* gnu/system/linux-initrd.scm (expression-&gt;initrd)[import-module?]: New
procedure.
[builder]: Pass it to 'source-module-closure'.
* gnu/system/install.scm (cow-store-service-type)[import-module?]: New
procedure.  Pass it to 'source-module-closure'.
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2020-11-21 12:39:14 +0100'>2020-11-21</span></td><td><a href='/guix/commit/gnu/build/linux-initrd.scm?id=2200bb214690ebc78b9fa42887ac9dfb8035bd4f'>linux-initrd: Remove unnecessary timestamp reset phase.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/build/linux-initrd.scm (write-cpio-archive): Mention timestamps in
docstring.
(build-initrd): Remove unnecessary timestamp reset phase.
</span></span></td><td>Ludovic Courtès</td></tr>