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=f0f53a817ab4c1d5052d12df9b9a7c6befb9cd65'>root</a>/<a href='/guix/log/tests?id=f0f53a817ab4c1d5052d12df9b9a7c6befb9cd65'>tests</a>/<a href='/guix/log/tests/ui.scm?id=f0f53a817ab4c1d5052d12df9b9a7c6befb9cd65'>ui.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/ui.scm?id=f0f53a817ab4c1d5052d12df9b9a7c6befb9cd65&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2020-03-25 16:02:53 +0100'>2020-03-25</span></td><td><a href='/guix/commit/tests/ui.scm?id=c136da3fbd92a5db1f889d37f0a7c938ccd63648'>tests: Adjust to 'show-manifest-transaction' changes.</a><span class='msg-avail'>...<span class='msg-tooltip'>This is a followup to 3e5ab0a7a9399bb098b9ced46bf3cbf4085c6bab.

* tests/ui.scm ("show-manifest-transaction"): Update regexp.
* tests/guix-package.sh: Adjust Emacs regexp in --with-source test.
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2020-02-23 12:47:13 +0100'>2020-02-23</span></td><td><a href='/guix/commit/tests/ui.scm?id=fa99c4bbc7acdb8def9ce14a05aacb73f99fe3b1'>ui: (size-&gt;number "1.M") is correctly parsed.</a><span class='msg-avail'>...<span class='msg-tooltip'>Reported by Pierre Neidhardt &lt;mail@ambrevar.xyz&gt;.

* guix/ui.scm (size-&gt;number)[unit-pos]: Add #\. to CHAR-SET:DIGIT.
* tests/ui.scm ("size-&gt;number, 1.M"): New test.
</span></span></td><td>Ludovic Courtès</td></tr>