[graphite] Fix pr38515: Disabling PPL/CLOOG with configure does not work

[Paolo Bonzini]

Sebastian Pop wrote:
> Hi,
> 
> With this patch, one can build 4.4 also without PPL/CLOOG even if they
> are installed
> by using --without-ppl, --without-cloog, --disable-ppl, or --disable-cloog.
> Okay for trunk after regstrap?

Yes.

Paolo