`FEAT_CPA` (Checked Pointer Arithmetic) adds pointer arithmetic
instructions that, on overflow out of the address bits, force bit 54 to
disagree with bit 55. This makes the result non-canonical so it faults
when dereferenced.

For readable decompilation these are lifted as if the instructions are
supported but enforcement is disabled (i.e., as if the CPU supports
`FEAT_CPA` but not `FEAT_CPA2`).