ir/aarch64: emit cbz/cbnz instead of cmp + b.ne

[henderkes]

ir_emit_if_int used to emit

cmp   w1, #0
b.ne  >refcount_path

and now emits

cbnz  w1, >refcount_path

for

function f($x) {
    $s = "s" . $x;   // $s is a refcounted string
    unset($s);       // FREE: DELREF + maybe destroy, only if refcounted
}

LLM disclosure: this was fully found and done by Fable, all I did was verify correctness. ~ +1% in jit on phpbench for both Clang and GCC. No non-jit impact for obvious reasons.

[Girgias]

Shouldn't this be opened against https://github.com/dstogov/ir ?

[henderkes]

The file doesn't mention anything like that, but it certainly seems like the files are copied over. I'll copy it over there, thank you!