swi-prolog-lite and gmp

["Lieven De Keyzer" <lieven.dekeyzer%gmail.com@localhost>]

I'm trying to build lang/swi-prolog-lite. During the configuration
phase I receive this message:

****************************************************************
* Could not find libgmp or gmp.h.  GMP enables SWI-Prolog
* support for unbounded integer arithmetic and rational numbers.
*
* See README.gmp for details.
****************************************************************.

However, I have installed devel/gmp.