Tolk: Constant folding of negative shift emits `PUSHNAN` instead of preserving runtime exception

[Gusarich]

The compiler folds 1 << -1 into PUSHNAN at compile time, but the equivalent runtime operation throws range_chk (exit code 5). This changes observable behavior based on whether the shift amount is a constant.

const BAD_SHIFT: int = 1 << -1;

@noinline
fun const_val(): int {
    return BAD_SHIFT;
}

@noinline
fun runtime_val(shift: int): int {
    return 1 << shift;
}

fun onInternalMessage(): (int, int) {
    return (const_val(), runtime_val(-1));
}

Compiles to:

const_val() PROC:<{
  PUSHNAN                 // const path: silently returns NaN
}>

runtime_val() PROC:<{  //  shift
  POW2                    // runtime path: throws for shift=-1
}>

onInternalMessage() PROC:<{
  const_val() CALLDICT
  -1 PUSHINT
  runtime_val() CALLDICT
}>

The runtime path throws exit code 5 (integer out of range) because POW2 range-checks its argument. The constant-folded version bypasses this and silently produces NaN.

Same input, different behavior. The compiler should reject 1 << -1 at compile time rather than folding it to NaN.