Compiler segfauts when shifting by a vector with an undefined value

### Zig Version

0.15.0-dev.936+fc2c1883b

### Steps to Reproduce and Observed Behavior

https://zig.godbo.lt/z/5xhenbabn
```zig
export fn foobar(x: @Vector(16, u8)) @Vector(16, u8) {
    return x >> @as(@Vector(16, u3), 
        .{ 0, 1, 2, 3, 4, 5, 6, 0, 0,  1,  2,  3,  4,  5,  6, undefined }
    );
}
```

It segfaults

### Expected Behavior

I expect no segfault