8xy7 still has test gaps

[gulrak]

When having a (wrong) 8xy7 implementation of the type:

    v[x] = (v[y] - v[x]);
    v[15] = (v[y] > v[x]);

the test suite still reports this as all fine. The issue is, that
this mostly works, but fails when x==y, leading to a wrong
flag result. This case is not tested so the flags test accepts
this wrong variant.