[IR][FIX] Intrinsics - don't apply default willreturn if IntrNoReturn is specified

Summary: Since willreturn will soon be added as default attribute, we can end up with both noreturn and willreturn on the same intrinsic. This was exposed by llvm.wasm.throw which has IntrNoReturn.

Reviewers: jdoerfert, arsenm

Differential Revision: https://reviews.llvm.org/D88644