yp_get_default_domain not found when linking gdm

[Michael Lea <mikel softmed com>]

I'm running Debian potato at home with most of CVS gnome 
installed.  However, I can't seem to get gdm to compile.  When it tries
to link, I get "function yp_get_default_domain not found".  In looking 
through altavista, I found that this function used to be in libc5, but has
been moved to libnsl.  However, I can't seem to find libnsl!  Is this a
problem
with gnome, or is it a problem with my debian setup?