- Update to new upstream version (0.15.7)
    - Do not build from git snapshot anymore. Rather, got the tarball from
        ftp://gcc.gnu.org/pub/gcc/infrastructure/cloog-ppl-0.15.7.tar.gz
    - The upstream tarball is named cloog-ppl, not cloog. Adjusted thusly.
    - Use system libtool to disable standard rpath
    - Do not try to touch the info file if it's not present. Closes #515929.