libmemcached 4.0 build fails

[Bradley Giesbrecht]

What's weird is if I remove configure --prefix=${prefix} libmemcached  
builds.

configure {
	system "cd $(worksrcpath) && ./configure"
}

without this I build ends with:

   CCLD   tests/atomsmasher
Undefined symbols:
   "___sync_fetch_and_add", referenced from:
       _ms_reconn_socks in ms_conn.o
       _ms_verify_value in ms_conn.o
       _ms_verify_value in ms_conn.o
       _ms_build_udp_headers in ms_conn.o
       _ms_mcd_mlget in ms_conn.o
       _ms_setup_conn in ms_conn.o
       _ms_mcd_set in ms_conn.o
       _ms_mcd_set in ms_conn.o
       _ms_mcd_get in ms_conn.o
       _ms_drive_machine in ms_conn.o
       _ms_drive_machine in ms_conn.o
       _ms_drive_machine in ms_conn.o
       _ms_drive_machine in ms_conn.o
       _ms_drive_machine in ms_conn.o
       _ms_drive_machine in ms_conn.o
       _ms_exec_task in ms_task.o
       _ms_exec_task in ms_task.o
       _ms_exec_task in ms_task.o
       _ms_exec_task in ms_task.o
       _ms_exec_task in ms_task.o
       _ms_exec_task in ms_task.o
       _ms_clock_handler in ms_thread.o
       _ms_clock_handler in ms_thread.o
       _ms_worker_libevent in ms_thread.o
       _ms_worker_libevent in ms_thread.o
       _ms_worker_libevent in ms_thread.o
   "___sync_fetch_and_sub", referenced from:
       _ms_conn_close in ms_conn.o
ld: symbol(s) not found
collect2: ld returned 1 exit status
make[2]: *** [clients/memslap] Error 1
make[2]: *** Waiting for unfinished jobs....
make[1]: *** [all-recursive] Error 1
make: *** [all] Error 2


// Brad