This patch allows us to use glibc's build system to build locales
in a package separate from glibc.

  1. Use 'localedef' from $PATH since we are not rebuilding it.
  2. Use '--no-archive' to avoid building the big locale archive, and
     because the already-built 'localedef' would want to write it
     to '/run/current-system/locale', which is not possible.
  3. Pass $(inst_complocaledir)/$$locale to install files in the right
     place, and because otherwise, 'localedef' fails with:
     "cannot write output files to `(null)'".

diff -ru glibc-2.29-old/localedata/Makefile glibc-2.29-new/localedata/Makefile
--- glibc-2.29-old/localedata/Makefile	2019-01-31 11:45:36.000000000 -0500
+++ glibc-2.29-new/localedata/Makefile	2019-07-03 22:48:35.662015071 -0400
@@ -385,7 +385,7 @@
 
 # Sometimes the whole collection of locale files should be installed.
 LOCALEDEF=I18NPATH=. GCONV_PATH=$(common-objpfx)iconvdata LC_ALL=C \
-$(rtld-prefix) $(common-objpfx)locale/localedef
+  localedef --no-archive
 install-locales: install-locale-archive
 
 # Create and install the locale-archive file.
@@ -414,7 +414,7 @@
 	input=`echo $$locale | sed 's/\([^.]*\)[^@]*\(.*\)/\1\2/'`; \
 	$(LOCALEDEF) $$flags --alias-file=../intl/locale.alias \
 		     -i locales/$$input -f charmaps/$$charset \
-		     $(addprefix --prefix=,$(install_root)) $$locale \
+		     $(addprefix --prefix=,$(install_root)) $(inst_complocaledir)/$$locale \
 	&& echo ' done';
 endef
 
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<div class='path'>path: <a href='/guix/log/?id=6457985e39d794c0f44d953d475aa19c41025d00'>root</a>/<a href='/guix/log/tests?id=6457985e39d794c0f44d953d475aa19c41025d00'>tests</a>/<a href='/guix/log/tests/syscalls.scm?id=6457985e39d794c0f44d953d475aa19c41025d00'>syscalls.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/syscalls.scm?id=6457985e39d794c0f44d953d475aa19c41025d00&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2021-02-25 11:29:35 +0100'>2021-02-25</span></td><td><a href='/guix/commit/tests/syscalls.scm?id=7e9d9f28e997e7faad28cdd1c416be174d6986e7'>syscalls: Add 'mounts' and the &lt;mount&gt; record type.</a><span class='msg-avail'>...<span class='msg-tooltip'>* guix/build/syscalls.scm (&lt;mount&gt;): New record type.
(option-string-&gt;mount-flags, mount-flags)
(octal-decode, mounts): New procedures.
(mount-points): Rewrite in terms of 'mount'.
* tests/syscalls.scm ("mounts"): New test.
</span></span></td><td>Ludovic Courtès</td></tr>