ipsec-tools searches for the kernel include files in directorys that dont exist on machines that dont have module support in the kernel. checking for /lib/modules/2.6.1-rc1/build/include/linux/pfkeyv2.h... no checking for /usr/src/devel-2.5/devel/include/linux/pfkeyv2.h... no of course this could be fixed with a symlink, but I think a fix in the configure scripts would be more clean.
On my system, adding this to the ebuild made it compile with kernel module support disabled: /usr/portage/net-firewall/ipsec-tools/ipsec-tools-0.2.2.ebuild: line 24 was: ./configure --prefix=/usr --sysconfdir=/etc || die line 24 new: ./configure --prefix=/usr --sysconfdir=/etc --with-kernel-headers=/usr/src/linux/include || die
This was fixed two weeks ago for all the ipsec-tools ebuilds. Thanks.