glibcLocales: also build C.UTF-8

Previously we only build C.UTF-8 as part of the locale-archive
that comes with the glibc core package.
However for consistent use of LANG=C.UTF-8 we also want support
in our glibcLocales as well.
fixes https://github.com/NixOS/nixpkgs/issues/57974

pkgs/development/libraries/glibc/locales.nix

@@ -26,6 +26,8 @@ callPackage ./common.nix { inherit stdenv; } {
     ''
       mkdir -p $TMPDIR/"${buildPackages.stdenv.cc.libc.out}/lib/locale"
 
+      echo 'C.UTF-8/UTF-8 \' >> ../glibc-2*/localedata/SUPPORTED
+
       # Hack to allow building of the locales (needed since glibc-2.12)
       sed -i -e 's,^$(rtld-prefix) $(common-objpfx)locale/localedef,localedef --prefix='$TMPDIR',' ../glibc-2*/localedata/Makefile
     ''