Update to 5.1

[root]

Hello,

I'm trying to update my 4.8 STABLE FreeBSD box to RELENG_5_1_0_RELEASE and
I get the following errors when making buildworld

building shared library libkse.so.1
thr_libc.So: In function `sigaction':
thr_libc.So(.text+0x54): multiple definition of `_sigaction'
thr_sigaction.So(.text+0x0): first defined here
thr_libc.So: In function `sigprocmask':
thr_libc.So(.text+0x34): multiple definition of `_sigprocmask'
thr_sigprocmask.So(.text+0x0): first defined here
*** Error code 1

Stop in /usr/src/lib/libpthread.
*** Error code 1

Stop in /usr/src/lib.
*** Error code 1

Any idea whats wrong with that ? I just cvsuped to RELENG_5_1_0_RELEASE.
This is what I'm running now
FreeBSD core-E3.valcea.net 4.8-STABLE FreeBSD 4.8-STABLE #33: Sat Jul  5 23:20:40 EEST 2003     root at core-E3.valcea.net:/usr/obj/usr/src/sys/CUSTOM  i386

Thanks,

Marian