Oh. You can do one of four (4) things :
Fix it yourself. Technical details on how ports work can be found in Porting applications.
Gripe. This is done by e-mail only! Send such e-mail to the maintainer of the port, first. Type make maintainer or read the Makefile to find the maintainer's email address. Remember to include the name/version of the port (copy the $FreeBSD: line from the Makefile), and the output leading up-to the error, inclusive. If you do not get a satisfactory response, you can try filing a bug report with send-pr.
Forget it. This is the easiest for most --- very few of the programs in ports can be classified as essential!
Grab the pre-compiled package from a ftp server. The ``master'' package collection is on FreeBSD's FTP server in the packages directory, though check your local mirror first, please! These are more likely to work (on the whole) than trying to compile from source and a lot faster besides! Use the pkg_add(1) program to install a package file on your system.