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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<tr><td><span title='2022-05-12 19:27:59 +0200'>2022-05-12</span></td><td><a href='/guix/commit/doc/images/gcc-core-mesboot0-graph.dot?id=eeba993f570483345acd59c2d8709fd5d7ee7ae7'>doc: Add the "Full-source Bootstrap".</a><span class='msg-avail'>...<span class='msg-tooltip'>* doc/guix.texi (Reduced Binary Seed Bootstrap): Update and rename to...
(Full-Source Bootstrap): ...this.
* doc/images/gcc-core-mesboot0-graph.dot: Regenerate.
</span></span></td><td>Jan (janneke) Nieuwenhuizen</td></tr>
<tr><td><span title='2020-05-22 16:11:52 +0200'>2020-05-22</span></td><td><a href='/guix/commit/doc/images/gcc-core-mesboot0-graph.dot?id=cd5d5f53228fd5bf96d9f790aa2606ae71fa68d7'>doc: Update 'Bootstrapping' for further binary seed reduction.</a><span class='msg-avail'>...<span class='msg-tooltip'>* doc/images/gcc-core-mesboot0-graph.dot: New image, replacing
* doc/images/gcc-mesboot0-bag-graph.dot: ... remove file.
* doc/local.mk (DOT_FILES): Update for new image file.
* doc/guix.texi (Reduced Binary Seed Bootstrap): Use it in updated description
of further reduction of the trusted computing base.
</span></span></td><td>Jan Nieuwenhuizen</td></tr>