/lib/pthread.so.2 is sought during some port compilation

[Yuri]

I tried to compile firefox-2.0.0.10 on 7.0-BETA3.
And one linking command failed seeking for malloc_lock symbol required by
/lib/pthread.so.2. Obviously it tried to link obsolete /lib/pthread.so.2 with
the new /lib/libc.so.7.

By reading /usr/src/UPDATING I learn that the default threading library has been
replaced by /lib/libthr.so.

Why would linker seek for libpthread.so instead of libthr.so?

Yuri