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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<tr><td><span title='2020-04-08 10:24:02 +0200'>2020-04-08</span></td><td><a href='/guix/commit/gnu/installer/newt/parameters.scm?id=ee0ad7803c82383ac1bced073d8670bc407797e7'>installer: Add proxy support.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/installer/proxy.scm: New file.
* gnu/local.mk (INSTALLER_MODULES): Add it.
* po/guix/POTFILES.in: Add it.
* gnu/installer/newt/parameters.scm (run-proxy-page): New procedure,
(run-parameters-page): add the previous procedure to the parameters menu.
</span></span></td><td>Mathieu Othacehe</td></tr>
<tr><td><span title='2020-04-08 10:24:02 +0200'>2020-04-08</span></td><td><a href='/guix/commit/gnu/installer/newt/parameters.scm?id=07a53bd512530d8f87e076263227216c467727bb'>installer: Turn help menu into parameters menu.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/local.mk (INSTALLER_MODULES): Rename help.scm into parameters.scm.
* po/guix/POTFILES.in: Ditto.
* gnu/installer/record.scm (&lt;installer&gt;): Rename help-menu into parameter-menu
and help-page into parameters-page.
* gnu/installer/newt/parameters.scm: Renamed from help.scm. Update information
messages.
* gnu/installer/newt.scm: Update accordingly.
* gnu/installer/newt/keymap.scm: Ditto.
</span></span></td><td>Mathieu Othacehe</td></tr>