Fix wrong isl version in 005-gcc.
The 005-gcc script contains an incorrect version reference for the isl external library. The file currently references isl-0.24.tar.bz2, but should reference isl-0.27.tar.bz2.
The 005-gcc script contains an incorrect version reference for the isl external library. The file currently references isl-0.24.tar.bz2, but should reference isl-0.27.tar.bz2.