Add new field PermuteOperands to mapping different operand order between C/C++ API and clang builtin.
Authored-by: Roger Ferrer Ibanez <rofirrim@gmail.com>
Co-Authored-by: Hsiangkai Wang <kai.wang@sifive.com>
Co-Authored-by: Zakk Chen <zakk.chen@sifive.com>
Not sure if we want to clarify that when this list is empty, the permutation is assumed to be equivalent to [0, 1, 2, 3, ...].