[CodeGen] Add support for multiple memory operands in MachineInstr::mayAlias

Summary:
To support all targets, the mayAlias member function needs to support instructions with multiple operands.

This revision also changes the order of the emitted instructions in some test cases.

Reviewers: efriedma, hfinkel, craig.topper, dmgreen

Reviewed By: efriedma

Subscribers: MatzeB, dmgreen, hiraditya, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D80161