[SCCP] Replace new value's value state with removed value's

In replaceSignedInst, if a signed instruction can be repalced with
unsigned instruction, we created a new instruction and removed the old
instruction's value state. If the following instructions has this new
instruction as a use operand, transformations like replaceSignedInst and
refineInstruction would be blocked. The reason is there is no value
state for the new instrution.

This patch set the new instruction's value state with the removed
instruction's value state. I believe it is correct bacause when we
repalce a signed instruction with unsigned instruction, the value state
is not changed.

Reviewed By: nikic

Differential Revision: https://reviews.llvm.org/D152337