[STATEPOINT] Force implicit-def for lr register.

[STATEPOINT] Force implicit-def for lr register.

STATEPOINT instruction behavior is similar to call instruction.
In aarch64 BL instruction implicitly define lr register, so
STATEPOINT instruction should do the same.
However STATEPOINT is a general pseudo instruction and I could not find
a way to override list of implicit defs for specific target.

So this patch post processes inserting STATEPOINT instruction by
adding implisit dead def for lr.

Reviewers: reames, loicottet, ostannard
Reviewed By: reames
Subscribers: danilaml, hiraditya, kristof.beyls, llvm-commits, yrouban
Differential Revision: https://reviews.llvm.org/D111114