[AArch64InstrInfo] Ignore debug insts in areCFlagsAccessedBetweenInstrs [7/14]

Summary:
Fix an issue where the presence of debug info could disable a peephole
optimization due to areCFlagsAccessedBetweenInstrs returning the wrong
result.

In test/CodeGen/AArch64/arm64-csel.ll, the issue was found in the
function @foo5, in which the first compare could successfully be
optimized but not the second.

Reviewers: t.p.northover, eastig, paquette

Subscribers: kristof.beyls, hiraditya, danielkiss, aprantl, dsanders, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D78157