change default compiler version to build an rpm

["Gianluca Cecchi" <gianluca cecchi gmail com>]

I have an FC5 system and problems running rpmbuild for a program with
default gcc that is  4.1.0.
I have the compat-gcc-32 package installed on my system.
Getting the source tgz file, setting CC with
export CC=gcc32
and then running configure and make it works and I can compile the
program, but I am not able to replicate this in spec file for
rpmbuild.

So I'm trying to change compiler settings from gcc to gcc32.
I added into the spec file the line
BuildRequires:  compat-gcc-32

but I'm not able to have the gcc32 set up.
I tried something like
%define %{__cc} gcc32
before the prep and build steps, but in
%configure step in build phase
I see that the detected compiler is gcc and not gcc32.
Any hints and pointers about macro redefinitions?
Thanks in advance,
Gianluca