error when building kernel source : unifdef is needed by kernel-2.6.18-1.2798.x86_64

["Ian Brown" <ianbrn gmail com>]

Hello,
I followed the instructions in
http://www.mjmwired.net/resources/mjm-fedora-fc6.html#kernelsrc
for installing and builing kernel source for Fodora Core 6  on x86_64.

I did my actions as a root and not as a user.

I download kernel-2.6.18-1.2798.fc6.src.rpm

I ran : rpm  -ivh kernel-2.6.18-1.2798.fc6.src.rpm
then :

rpmbuild -bp --target=x86_64 kernel-2.6.spec
Building target platforms: x86_64
Building for target x86_64
error: Failed build dependencies:
       unifdef is needed by kernel-2.6.18-1.2798.x86_64
and I have nothing in  /usr/src/redhat/BUILD/

googling for this error gave only 1 hit:
 http://www.t2-project.org/irclogs/t2-2006-10-17
and it did not help much.


Any idea what could it be ? did anyone tried and had success with it ?
Regards,
IB