gnu: gdm: Change locale settings file.

* gnu/packages/gnome.scm (gdm)[arguments]: Set the '--with-lang-file'
configure flag to '/etc/environment'.

Signed-off-by: Danny Milosavljevic <dannym@scratchpost.org>

gnu/packages/gnome.scm

@@ -5338,6 +5338,10 @@ libxml2.")
          ;; script. It provides a generic one if --enable-gdm-xsession is set.
          "--enable-gdm-xsession"
 
+         ;; Use '/etc/environment' for locale settings instead of the
+         ;; systemd-specific '/etc/locale.conf'.
+         "--with-lang-file=/etc/environment"
+
          "--localstatedir=/var"
          ,(string-append "--with-default-path="
                          (string-join '("/run/setuid-programs"