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.

interface Iin
{
    void[] read(size_t n);
}

interface Iout
{
    size_t write(void[] d);
}

class C : Iin
{
    void[] read(size_t n)
    {
        return null;
    }

    size_t write(void[] d)
    {
        return 0;
    }
}

void main()
{
    scope c = new C;
}