Milter-greylist

I am trying to compile milter-greylist v 

I run:
./configure  --with-libGeoIP --prefix=/usr --with-libpthread=/usr/lib/

And the output I get is:


If I leave off all config options, it works just fine.

checking for pthread_create in -lpthread... no
checking for pthread_create in -lc_r... no
checking for pthread_create in -lpthreads -lpthread... no
Required libpthread not found. Use --with-libpthread


libpthread is in /usr/lib.

Can anyone help?

My system is CentOS 4.

John