"make depend" fails, cc1: no such file

[Stephen G Smith]

I am running FreeBSD 5.1-RELEASE, and I want to add firewall support to
my kernel. So, I carefully read and followed the instructions in section
9.3 of the FreeBSD Handbook. But when I run "make depend" i get this
error:

cc: installation problem, cannot exec 'cc1': no such file or directory
*** Error code 1

I know I have a file /usr/bin/cc, but obviously no 'cc1' anywhere.
Any hints?

Thanks,

Stephen