This is part of an effort to reduce the differences between the custom C++ bindings used right now by polly in lib/External/isl/include/isl/isl-noxceptions.h and the official isl C++ interface.
- Removing method to_str() from all the classes in the isl C++ bindings.
- Overload method stringFromIslObj() so it accepts isl C++ objects.
- To keep backward compatibility stringFromIslObj() now accepts a value that is returned if the isl C object is null or doesn't have a string representation (by default it's an empty string). In some cases it's better to have the string "null" instead of an empty string.
- isl-noexceptions.h has been generated by this https://github.com/patacca/isl/commit/d33ec3a3bbaf971b254a853e6d8200ff9f5a1385