maint: fix message translation glitches

Problem reported by Sebastian Rasmussen in: http://bugs.gnu.org/18054
* gl/lib/randread.c (randread_error): Don't put multiple string
literals inside _(...), as xgettext doesn't support that.
* src/chroot.c (main): In diagnostics, don't bother to distinguish
between setting the number of supplemental group IDs to a zero or
to a nonzero value, as the underlying system call is the same
either way.  This also makes the string easier to translate correctly.

gl/lib/randread.c

@@ -125,7 +125,7 @@ randread_error (void const *file_name)
 {
   if (file_name)
     error (exit_failure, errno,
-           _(errno == 0 ? "%s: end of file" : "%s: read error"),
+           errno == 0 ? _("%s: end of file") : _("%s: read error"),
            quotearg_colon (file_name));
   abort ();
 }

src/chroot.c

@@ -392,8 +392,7 @@ main (int argc, char **argv)
 #endif
 
   if ((uid_set (uid) || groups) && setgroups (n_gids, gids) != 0)
-    error (EXIT_CANCELED, errno, _("failed to %s supplemental groups"),
-           gids ? "set" : "clear");
+    error (EXIT_CANCELED, errno, _("failed to set supplemental groups"));
 
   free (in_gids);
   free (out_gids);