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=e525c866d38b6c7498375f38eea7c92b0f7b6a4f'>root</a>/<a href='/guix/log/gnu?id=e525c866d38b6c7498375f38eea7c92b0f7b6a4f'>gnu</a>/<a href='/guix/log/gnu/installer?id=e525c866d38b6c7498375f38eea7c92b0f7b6a4f'>installer</a>/<a href='/guix/log/gnu/installer/aux-files?id=e525c866d38b6c7498375f38eea7c92b0f7b6a4f'>aux-files</a>/<a href='/guix/log/gnu/installer/aux-files/logo.txt?id=e525c866d38b6c7498375f38eea7c92b0f7b6a4f'>logo.txt</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/gnu/installer/aux-files/logo.txt?id=e525c866d38b6c7498375f38eea7c92b0f7b6a4f&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2019-01-17 14:04:20 +0100'>2019-01-17</span></td><td><a href='/guix/commit/gnu/installer/aux-files/logo.txt?id=d0f3a672dcbdfefd3556b6a21985ff0e35eed3be'>gnu: Add graphical installer support.</a><span class='msg-avail'>...<span class='msg-tooltip'>* configure.ac: Require that guile-newt is available.
* gnu/installer.scm: New file.
* gnu/installer/aux-files/logo.txt: New file.
* gnu/installer/build-installer.scm: New file.
* gnu/installer/connman.scm: New file.
* gnu/installer/keymap.scm: New file.
* gnu/installer/locale.scm: New file.
* gnu/installer/newt.scm: New file.
* gnu/installer/newt/ethernet.scm: New file.
* gnu/installer/newt/hostname.scm: New file.
* gnu/installer/newt/keymap.scm: New file.
* gnu/installer/newt/locale.scm: New file.
* gnu/installer/newt/menu.scm: New file.
* gnu/installer/newt/network.scm: New file.
* gnu/installer/newt/page.scm: New file.
* gnu/installer/newt/timezone.scm: New file.
* gnu/installer/newt/user.scm: New file.
* gnu/installer/newt/utils.scm: New file.
* gnu/installer/newt/welcome.scm: New file.
* gnu/installer/newt/wifi.scm: New file.
* gnu/installer/steps.scm: New file.
* gnu/installer/timezone.scm: New file.
* gnu/installer/utils.scm: New file.
* gnu/local.mk (GNU_SYSTEM_MODULES): Add previous files.
* gnu/system.scm: Export %root-account.
* gnu/system/install.scm (%installation-services): Use kmscon instead of linux
VT for all tty.
(installation-os)[users]: Add the graphical installer as shell of the root
account.
[packages]: Add font related packages.
* po/guix/POTFILES.in: Add installer files.
</span></span></td><td>Mathieu Othacehe</td></tr>