Stage2 miscompiles vector element acces via slice of vectors

```zig
// pub export fn entry() void {
test {
    @setRuntimeSafety(false);
    var small_bases = [2]@Vector(2, u8){
        @Vector(2, u8){ 0, 1 },
        @Vector(2, u8){ 2, 3 },
    };
    var a: []const @Vector(2, u8) = &small_bases;
    var a4 = a[1][1];
    _ = a4;
}
```
```
Test [1/1] test_0... error: the following test command crashed:
```