Configure script for gcc 4.7.2 fails with no ppl

[Steve Lorimer]

I'm trying to configure GCC 4.7.2, but it's failing with configure:
error: Unable to find a usable PPL

I've looked in GCC prerequisites page and PPL isn't mentioned anywhere.

I'm using CLooG 0.17.0, which uses ISL, and as such no longer requires
PPL (as far as I can tell)

Is there some other requirement on PPL in GCC which means I still need
PPL, or am I missing some flag from my configure line?

I am passing the following options to configure:

--enable-cloog-backend=isl
--with-cloog=$PREFIX
--with-isl=$PREFIX
--with-gmp=$PREFIX
--with-mpfr=$PREFIX
--with-mpc=$PREFIX

Thanks
Steve