[polly] isl-only polly build in cmake

    Do we have cmake flags to set with -D that will allow polly to build
as isl-only (with using cloog) yet? Thanks in advance for any info.

In case you do not provide a path to cloog or you set the cloog library and include paths explicitly to CLOOG_INCLUDE_DIR-NOTFOUND and CLOOG_LIBRARY-NOTFOUND Polly should be built without CLooG. I did not test this recently, but Sebastian is running this setup regularly.