Fix interaction of CFI instructions with MachineOutliner.

1. When checking if a candidate contains a CFI instruction, actually
iterate over all of the instructions, instead of stopping halfway
through.
2. Make sure copied CFI directives refer to the correct instruction.

Fixes https://github.com/llvm/llvm-project/issues/55842

Differential Revision: https://reviews.llvm.org/D126930