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
--- a/localedata/Makefile
+++ b/localedata/Makefile
@@ -176,7 +176,8 @@
 else
 install-others := $(addprefix $(inst_i18ndir)/, \
 			      $(addsuffix .gz, $(charmaps)) \
-			      $(locales))
+			      $(locales)) \
+                   $(inst_i18ndir)/SUPPORTED
 endif
 
 tests: $(objdir)/iconvdata/gconv-modules
@@ -401,6 +402,14 @@
 
 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=851cabc35bc81974c399aadb02bd98bf00eda529'>root</a>/<a href='/guix/log/tests?id=851cabc35bc81974c399aadb02bd98bf00eda529'>tests</a>/<a href='/guix/log/tests/containers.scm?id=851cabc35bc81974c399aadb02bd98bf00eda529'>containers.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/tests/containers.scm?id=851cabc35bc81974c399aadb02bd98bf00eda529&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2020-10-01 12:51:13 +0200'>2020-10-01</span></td><td><a href='/guix/commit/tests/containers.scm?id=e74818353882f187e5971b5a3a481f17df883dbe'>linux-container: Reset jailed root permissions.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/build/linux-container.scm (mount-file-systems): Add 'chmod' call.
* tests/containers.scm
("call-with-container, mnt namespace, root permissions"): New test.
</span></span></td><td>Jelle Licht</td></tr>
<tr><td><span title='2019-10-15 10:21:41 +0200'>2019-10-15</span></td><td><a href='/guix/commit/tests/containers.scm?id=e464ac667297d2acf57e52438a39cadc87b95da2'>tests: Skip container test when lacking kernel support.</a><span class='msg-avail'>...<span class='msg-tooltip'>This is a followup to 96b35998e610c7fc37bf87bf9e07e63d3bebd0a3.

* tests/containers.scm ("eval/container, non-empty load path"): Add
missing 'skip-if-unsupported' call.
</span></span></td><td>Ludovic Courtès</td></tr>