buildworld RELENG_5_1 on 4.9 fails

[Mario Sassmann]

>I tryed to update to RELENG_5_1 on RELENG_4_9, but make buildworld failed 
>(machine i386)
>
>cc -fpic -DPIC -O -pipe -march=pentium3 -DPTHREAD_KERNEL 
>-I/usr/src/lib/libpthread/../libc/include -I/usr/src/lib/libpthread/thread  
>-I/usr/src/lib/libpthread/../../include 
>-I/usr/src/lib/libpthread/arch/i386/include -I/usr/src/lib/libpthread/sys 
>-I/usr/src/lib/libpthread/../../libexec/rtld-elf -fno-builtin -D_LOCK_DEBUG 
>-D_PTHREADS_INVARIANTS -Wall  -c /usr/src/lib/libpthread/sys/lock.c -o 
>lock.So
>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
>
>Stop in /usr/src.
>*** Error code 1
>
>Stop in /usr/src.
>*** Error code 1
>
>Stop in /usr/src.
>*** Error code 1
>
>Stop in /usr/src.

Someone sent me a mail referable this problem. But I've lost my Mail-Directory 
=((
Unfortunately, now I'm not able to answer. Please could the one send a mail to 
me again?