Lower sin/cos operation in complex dialect to libm as a baseline. This follows up to https://reviews.llvm.org/D125550. Reviewed By: pifon2a Differential Revision: https://reviews.llvm.org/D126755
Lowering through libm gives us a baseline version, even though it's not going to be particularly fast. This is similar to what we do for some math dialect ops. Differential Revision: https://reviews.llvm.org/D125550