[LegalizeTypes] Add a simple expansion for SMULO when a libcall isn't available.

This isn't optimal, but prevents crashing when the libcall isn't
available. It just calculates the full product and makes sure the high bits
match the sign of the low half. Each of the pieces should go through their own
type legalization.

This can make D107420 unnecessary.

Needs tests, but I wanted to start discussion about D107420.

Reviewed By: FreddyYe

Differential Revision: https://reviews.llvm.org/D107581