Add initial parsing/sema support for new assumption clause so clause can
be specified. For now, it's ignored, just like the others.
Added support for 'no_openmp_construct' to release notes.
Testing
- Updated appropriate LIT tests.
- Testing: check-all
This pr implements the `[[omp::assume]]` spelling for the `__attribute__((assume))` attribute. It does not change anything about how that attribute is handled by the rest of Clang.