Fix error with automake 1.13+
Add isl and cloog-isl CMake modules (for CMake find_package function)

NB: the isl module is there for convenience purpose. If it appears
someday in isl itself, it should be removed.
Add osl extbody extension support
Fix include directory for libcloog-isl
Fix out of tree builds
Update to isl 0.12.1
CLooG 0.18.1

Signed-off-by: Tobias Grosser <tobias@grosser.es>