I noticed something similar on a RH7.3 box last night (current pkgsrc).
again libpthread.la was empty:

[root@dyslexia htdocs]# ls -l /usr/lib/libpthread.* /lib/libpthread*
-rwxr-xr-x    1 root     root        86848 Apr 15  2002 /lib/libpthread-0.9.so
lrwxrwxrwx    1 root     root           17 Nov 29 11:25 /lib/libpthread.so.0 -> libpthread-0.9.so
-rw-r--r--    1 root     root       118146 Apr 15  2002 /usr/lib/libpthread.a
lrwxrwxrwx    1 root     root           25 Nov 29 11:30 /usr/lib/libpthread.so -> ../../lib/libpthread.so.0

The .fake_la script does not know what to do if it does not find a .so.*
under /usr/lib/.

By adding a symlink for libpthread.so.0 under /usr/lib/ it continued on...

On Thu, 30 Jan 2003, Konrad Neuwirth wrote:

> Date: Thu, 30 Jan 2003 11:26:44 +0100
> From: Konrad Neuwirth <konrad@mailathome.or.at>
> To: Johnny C. Lam <jlam@netbsd.org>, current-users@netbsd.org
> Subject: Re: Failing to build glib
>
> > Can you post the contents of work/.buildlink/lib/libpthread.la?  I wrote
> > some of that stuff "blind" since I don't have a -current NetBSD system
> > on which to test.
>
> Here we go:
>
> | [konrad@amelie:/usr/pkgsrc/devel/glib/work/.buildlink/lib] ls -l
> | total 0
> | lrwxr-xr-x  1 root  wheel  21 Jan 30 03:23 libpthread.a -> /usr/lib/libpthread.a
> | -rw-r--r--  1 root  wheel   0 Jan 30 03:23 libpthread.la
> | [konrad@amelie:/usr/pkgsrc/devel/glib/work/.buildlink/lib]
>
> Cheers,
>  Konrad
>