glibc: support obsolete "compat" in nsswitch.conf

Fixes #31700. See https://bugs.archlinux.org/task/54592.

pkgs/development/libraries/glibc/common.nix

···
   configureFlags =
     [ "-C"
       "--enable-add-ons"
+      "--enable-obsolete-nsl"
       "--enable-obsolete-rpc"
       "--sysconfdir=/etc"
       "--enable-stackguard-randomization"