This is directly available in TargetInstrInfo

Add per-property has<Prop>/set<Prop>/reset<Prop> functions to
MachineFunctionProperties.

These are the the ones where we already had a Register object being
used. Some places are still using unsigned which I did not convert.

Identified with misc-include-cleaner.

Track the live register state immediately before, instead of after,
MBBI. This makes it simple to track the state at the start or end of a
basic block without a separate (and poorly named) Tracking flag.

This changes the API of the backward(MachineBasicBlock::iterator I)
method, which now recedes to the state just before, instead of just
after, *I. Some clients are simplified by this change.

There is one small functional change shown in the lit tests where
multiple spilled registers all need to be reloaded before the same
instruction. The reloads will now be inserted in the opposite order.
This should not affect correctness.

Differential Revision: https://reviews.llvm.org/D156987

Reviewed By: foad

Differential Revision: https://reviews.llvm.org/D152098

All users have been converted to scavengeRegisterBackwards.

Differential Revision: https://reviews.llvm.org/D152425

This matches what scavengeRegisterBackwards does.

This is in preparation for converting most uses of scavengeRegister to
scavengeRegisterBackwards, to reduce test case churn when that lands and
to help with bisection if anything goes wrong.

Differential Revision: https://reviews.llvm.org/D150792