This patch is taken from debian's glibc package (generate-supported.mk).
It install the localedata/SUPPORTED file of the glibc. This file lists
all the supported locales of the glibc.

diff --git a/localedata/Makefile b/localedata/Makefile
index 65079f9eb8..14818f84e0 100644
--- a/localedata/Makefile
+++ b/localedata/Makefile
@@ -169,7 +169,8 @@ endif
 # Files to install.
 install-others := $(addprefix $(inst_i18ndir)/, \
 			      $(addsuffix .gz, $(charmaps)) \
-			      $(locales))
+			      $(locales)) \
+                   $(inst_i18ndir)/SUPPORTED
 
 tests: $(objdir)/iconvdata/gconv-modules
 
@@ -380,6 +381,14 @@ endif
 
 include SUPPORTED
 
+$(inst_i18ndir)/SUPPORTED: SUPPORTED $(+force)
+	for locale in $(SUPPORTED-LOCALES); do \
+		[ $$locale = true ] && continue; \
+		echo $$locale | sed 's,/, ,' >> LOCALES; \
+	done
+	$(make-target-directory)
+	$(INSTALL_DATA) LOCALES $@
+
 INSTALL-SUPPORTED-LOCALE-ARCHIVE=$(addprefix install-archive-, $(SUPPORTED-LOCALES))
 INSTALL-SUPPORTED-LOCALE-FILES=$(addprefix install-files-, $(SUPPORTED-LOCALES))
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<div class='path'>path: <a href='/guix/log/?id=c005550769f0703f0c844f2007ec09f96f000646'>root</a>/<a href='/guix/log/gnu?id=c005550769f0703f0c844f2007ec09f96f000646'>gnu</a>/<a href='/guix/log/gnu/tests.scm?id=c005550769f0703f0c844f2007ec09f96f000646'>tests.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/tests.scm?id=c005550769f0703f0c844f2007ec09f96f000646&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2020-07-25 19:11:36 +0200'>2020-07-25</span></td><td><a href='/guix/commit/gnu/tests.scm?id=a5e2fc73760a2ae023f2e56bdbf8025971f90e64'>utils: Move &lt;location&gt; and '&amp;error-location' to (guix diagnostics).</a><span class='msg-avail'>...<span class='msg-tooltip'>* guix/utils.scm (&lt;location&gt;, source-properties-&gt;location)
(location-&gt;source-properties, &amp;error-location): Move to...
* guix/diagnostics.scm: ... here.
* gnu.scm: Adjust imports accordingly.
* gnu/machine.scm: Likewise.
* gnu/system.scm: Likewise.
* gnu/tests.scm: Likewise.
* guix/inferior.scm: Likewise.
* tests/channels.scm: Likewise.
* tests/packages.scm: Likewise.
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2020-03-05 16:33:37 +0100'>2020-03-05</span></td><td><a href='/guix/commit/gnu/tests.scm?id=c0b726c2112e0e670dc134583b376541c0a3789a'>tests: Add &lt;system-test&gt; gexp compiler.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/tests.scm (compile-system-test): New gexp compiler.
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2020-01-23 11:26:55 +0100'>2020-01-23</span></td><td><a href='/guix/commit/gnu/tests.scm?id=f79313b3871ebe204c7b29fdb823666af06f48ff'>tests: Fix typo in comment.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/tests.scm: Add missing word in commentary.
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2019-12-18 22:36:37 +0100'>2019-12-18</span></td><td><a href='/guix/commit/gnu/tests.scm?id=ab7010af1f1077c056529769a53a380147c3933f'>gexp: Allow character literals in GEXP-&gt;SEXP.</a><span class='msg-avail'>...<span class='msg-tooltip'>Fixes &lt;https://bugs.gnu.org/38628&gt;.

* tests/gexp.scm ("lower-gexp, character literal"): New test.
* guix/gexp.scm (gexp-&gt;sexp)[self-quoting?]: Add CHAR? to the tested types.
* guix/repl.scm (self-quoting?): Likewise.
* gnu/tests.scm (marionette-shepherd-service)[self-quoting?]: Likewise.
</span></span></td><td>Marius Bakke</td></tr>
td><span title='2022-08-05 00:14:29 +0200'>2022-08-05</span></td><td><a href='/guix/commit/etc/disarchive-manifest.scm?id=2acffd56a58c01785ea6ea738b79991c0685d364'>disarchive-manifest: Handle tar.xz archives.</a><span class='msg-avail'>...<span class='msg-tooltip'>* etc/disarchive-manifest.scm (tarball-origin?): Add ".tar.xz".
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2021-10-09 01:02:18 +0200'>2021-10-09</span></td><td><a href='/guix/commit/etc/disarchive-manifest.scm?id=2ad1ef844632b7605ad6dd362e947a122a0a3925'>disarchive-manifest: Provide valid 'version' string.</a><span class='msg-avail'>...<span class='msg-tooltip'>* etc/disarchive-manifest.scm &lt;top level&gt;: Turn 'version' field into a
string.
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2021-09-14 11:50:58 +0200'>2021-09-14</span></td><td><a href='/guix/commit/etc/disarchive-manifest.scm?id=98712c14fe3517a48603a12eb2e64db305a54fe5'>etc: Add 'disarchive-manifest.scm'.</a><span class='msg-avail'>...<span class='msg-tooltip'>* etc/disarchive-manifest.scm: New file.
* Makefile.am (EXTRA_DIST): Add it.
</span></span></td><td>Ludovic Courtès</td></tr>