[Cranelift] Implement scalar min/max for AArch64

[sparker-arm]

The CLIF operators: umin, smin, imin and imax all support scalars, as well as vectors, but AArch64 currently only implements support for vectors. The backend will panic given the scalar versions.

[afonso360]

Hey, I just hit this with the fuzzer, Is there a reason as to why this is not planned?

[sparker-arm]

Oh... I don't remember closing this! Considering it happened on the same day, I'm assuming I did so by accident.

[sparker-arm]

Another realistic option, is that is a duplicate of another issue and I've just failed to link it.

[afonso360]

Fuzzgen just rediscovered this issue (for i128's) again on this CLIF input:

test compile
set opt_level=speed_and_size
target aarch64

function %a() -> i128 system_v {
block0:
    v83 = iconst.i64 0
    v0 = uextend.i128 v83  ; v83 = 0
    v80 = iconst.i64 0
    v3 = uextend.i128 v80  ; v80 = 0
    v4 = iconst.i8 0
    v6 = iconst.i64 0
    v40 = icmp slt v3, v0
    v58 = select v40, v0, v3
    v84 = iconst.i64 0
    v17 = uextend.i128 v84  ; v84 = 0
    v86 = iconst.i64 0
    v62 = uextend.i128 v86  ; v86 = 0
    brif v4, block1, block2(v0)  ; v4 = 0

block1 cold:
    brif.i64 v6, block2(v58), block2(v17)  ; v6 = 0

block2(v18: i128) cold:
    return v62
}

This is due to the rules added in #5546