[Statepoint Lowering] Add an option to allow use gc values in regs for landing pad

Default value is not changed, so it is NFC actually.

The option allows to use gc values on registers in landing pads.

Reviewers: reames, dantrushin
Reviewed By: reames, dantrushin
Subscribers: llvm-commits
Differential Revision: https://reviews.llvm.org/D94469