ports/net/asterisk build problem

[Wojciech Puchar]

ends with this at linking:
__sync_sub_and_fetch_4'
manager.o(.text+0x1c09): In function `accept_thread':
/usr2/ports/net/asterisk/work/asterisk-1.4.20.1/include/asterisk/lock.h:1118: 
undefined reference to `__sync_fetch_and_add_4'
manager.o(.text+0x4b5c): In function `action_waitevent':
/usr2/ports/net/asterisk/work/asterisk-1.4.20.1/include/asterisk/lock.h:1164: 
undefined reference to `__sync_sub_and_fetch_4'
manager.o(.text+0x6e8c): In function `generic_http_callback':
/usr2/ports/net/asterisk/work/asterisk-1.4.20.1/include/asterisk/lock.h:1118: 
undefined reference to `__sync_fetch_and_add_4'



anyone know where these __sync_* functions are?