[Polly][Isl] Removing nullptr constructor from C++ bindings. NFC.
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.
Changes made:
- Removed std::nullptr_t constructor from all the classes in the isl C++ bindings.
- isl-noexceptions.h has been generated by this https://github.com/patacca/isl/commit/a7e00bea38f251a4bcf5c2c6ce5fa7ee5f661528
clang-tidy: error: out-of-line definition of 'createPPCGCodeGenerationPass' does not match any declaration in namespace 'polly' [clang-diagnostic-error]
not useful