Adds a new method finalizeLowering to TargetLoweringBase. This is in preparation for an upcoming commit.
This function is meant for target specific adjustments to MachineFrameInfo or register reservations.
Move the freezeRegisters() and the hasCopyImplyingStackAdjustment() handling into the new function to prove the concept. As an added bonus GlobalISel no longer missed the hasCopyImplyingStackAdjustment() handling with this.
Can we move this to after ExpandISelPseudos at least? It's a problem that reserved registers are frozen this early