gnu: glibc: Export supported locales.

Debian and Archlinux (at least) force the installation of the
localedata/SUPPORTED file of the glibc. This file lists all the supported
locales of the glibc.

* gnu/packages/patches/glibc-supported-locales.patch: New file.
* gnu/local.mk (dist_patch_DATA): Add it.
* gnu/packages/base.scm (glibc/linux): Add the previous patch,
(glibc-2.28): ditto.

gnu/local.mk

@@ -763,6 +763,7 @@ dist_patch_DATA =						\
   %D%/packages/patches/glibc-versioned-locpath.patch		\
   %D%/packages/patches/glibc-2.27-git-fixes.patch		\
   %D%/packages/patches/glibc-2.28-git-fixes.patch		\
+  %D%/packages/patches/glibc-supported-locales.patch     	\
   %D%/packages/patches/glusterfs-use-PATH-instead-of-hardcodes.patch		\
   %D%/packages/patches/glog-gcc-5-demangling.patch		\
   %D%/packages/patches/gmp-arm-asm-nothumb.patch		\

gnu/packages/base.scm

@@ -604,7 +604,8 @@ store.")
                                      "glibc-hidden-visibility-ldconfig.patch"
                                      "glibc-versioned-locpath.patch"
                                      "glibc-allow-kernel-2.6.32.patch"
-                                     "glibc-reinstate-prlimit64-fallback.patch"))))
+                                     "glibc-reinstate-prlimit64-fallback.patch"
+                                     "glibc-supported-locales.patch"))))
    (build-system gnu-build-system)
 
    ;; Glibc's <limits.h> refers to <linux/limit.h>, for instance, so glibc
@@ -901,7 +902,8 @@ GLIBC/HURD for a Hurd host"
                                        "glibc-hidden-visibility-ldconfig.patch"
                                        "glibc-versioned-locpath.patch"
                                        "glibc-allow-kernel-2.6.32.patch"
-                                       "glibc-reinstate-prlimit64-fallback.patch"))))))
+                                       "glibc-reinstate-prlimit64-fallback.patch"
+				       "glibc-supported-locales.patch"))))))
 
 (define-public glibc-2.26
   (package

gnu/packages/patches/glibc-supported-locales.patch

@@ -0,0 +1,31 @@
+This patch is taken from debian's glibc package (generate-supported.mk).
+
+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.