[MachineVerifier] Add check that tied physregs aren't different.

Summary: Added MachineVerifier code to check register ties more thoroughly, especially so that physical registers that are tied are the same. This may help e.g. when creating MIR files.

Original patch by Jesper Antonsson

Reviewers: stoklund, sanjoy, qcolombet

Reviewed By: qcolombet

Subscribers: qcolombet, llvm-commits

Differential Revision: https://reviews.llvm.org/D34394

llvm-svn: 307259