Fix some unittests for 64-bit asm. They were operating on int variables as if they were longs. This was causing asm1_1 to fail when compiled with -O3 because it was overwriting the spilled value of callee-saved register %rbx, which the runtime was using as a pointer value at the time.

module bug7;

class love { }
void bug() {
    love[] child;
    child.length=1;
    assert(child[0] is null);
    child[0]=null;
    assert(child[0] is null);
}
void main()
{
    bug();
}