Cranelift: "constant immediate is out of bounds"

Adding this optimization to `codegen/src/opts/icmp.isle`

```
;; sge(x, c) == sgt(x, c-1), for c != SMIN.
(rule (simplify (sge (fits_in_64 (ty_int bty)) x (iconst cty (u64_from_imm64 c))))
(if-let $false (u64_eq c (ty_smin cty)))
(sgt bty x (iconst cty (imm64 (u64_sub c 1)))))
```

Triggers a verification error when optimizing `filetests/filetests/egraph/icmp-parameterized.clif`:
```
FAIL filetests/filetests/egraph/icmp-parameterized.clif: optimize

Caused by:
function %icmp_sgt_umax(i32) -> i8 fast {
block0(v0: i32):
v5 = iconst.i32 -1
; ^~~~~~~~~~~~~~~~~~
; error: inst5 (v5 = iconst.i32 -1): constant immediate is out of bounds

v10 = icmp sgt v0, v5 ; v5 = -1
return v10
}

; 1 verifier error detected (see above). Compilation aborted.
```

I suspect somewhere the immediate is being sign extended when it should be zero extended