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.old b/localedata/Makefile
index 34877c0..a61d9b9 100644
--- a/localedata/Makefile.old
+++ b/localedata/Makefile
@@ -91,7 +91,8 @@ endif
 # Files to install.
 install-others := $(addprefix $(inst_i18ndir)/, \
 			      $(addsuffix .gz, $(charmaps)) \
-			      $(locales))
+			      $(locales)) \
+                   $(inst_i18ndir)/SUPPORTED
 
 tests: $(objdir)/iconvdata/gconv-modules
 
@@ -195,6 +196,14 @@ 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 $@
+
 INSTALL-SUPPORTED-LOCALES=$(addprefix install-, $(SUPPORTED-LOCALES))
 
 # Sometimes the whole collection of locale files should be installed.
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<tr class='logheader'><td><span title='2020-03-22 16:49:47 +0100'>2020-03-22</span></td><td class='logsubject'><a href='/guix/commit/build-aux/hydra/evaluate.scm?id=9acacb71c958218fd69cf0fb9df0b439a980a0f2'>Remove workaround for 'time-monotonic' in Guile 2.2.2.</a></td><td>Ludovic Courtès</td></tr>
<tr class='nohover-highlight'><td/><td colspan='3' class='logmsg'>
This is a followup to e688c2df3924423b67892cc9939ca099c729d1cb.

* build-aux/hydra/evaluate.scm &lt;top level&gt;: Remove 'time-monotonic'
definition.
* guix/cache.scm: Likewise.
* guix/progress.scm: Likewise.
* guix/scripts/substitute.scm: Likewise.
* guix/scripts/weather.scm: Likewise.
* tests/cache.scm: Likewise.


</td></tr>
<tr class='logheader'><td><span title='2020-03-22 12:42:52 +0100'>2020-03-22</span></td><td class='logsubject'><a href='/guix/commit/build-aux/hydra/evaluate.scm?id=66a198c8075f02d7075a555b48dd3adde88ebbbf'>hydra: evaluate: Use 'with-build-handler'.</a></td><td>Ludovic Courtès</td></tr>
<tr class='nohover-highlight'><td/><td colspan='3' class='logmsg'>
* build-aux/hydra/evaluate.scm (command-line): Remove 'set!' for
'build-things'.  Use 'with-build-handler' instead.
* build-aux/hydra/gnu-system.scm (hydra-jobs): Add comment about
removing 'show-what-to-build' call.


</td></tr>