Rebase C++ bindings on top of latest isl bindings
The main difference in this change is that isl_stat is now always
checked by default. As we elminiated most used of isl_stat, thanks to
Philip Pfaffe's implementation of foreach, only a small set of changes
This change does not include the following recent changes to isl's C++
- stricter error handling for isl_bool
- dropping of the isl::namespace qualifiers
The former requires a larger patch in Polly and consequently should go
through a patch-review. The latter will be applied in the next commit to
keep this commit free from noise.
We also still apply a couple of other changes on top of the official isl
bindings. This delta is expected to shrink over time.