This is part of the series started by D68484.
This pass moves llvm.noalias intrinsics to the noalias_sidechannel path of
load/store instructions. At the same time, they are converted into
llvm.side.noalias intrinsics. For llvm.noalias intrinsics that are
returned or passed as arguments, a llvm.noalias.arg.guard is introduced,
combining the pointer path and the noalias_sidechannel path.
This migration allows other optimization passes to do changes on the
normal pointer path, without impacting the noalias_sidechannel path that
contains the restrict/noalias related information.
Note: this is a stable point and tests should run fine with the patches applied up to this point.