6901 – wrong error "override cannot be applied to variable" in CTFE forward reference

Applies to both D1 and D2, at least as far back as 2.040. It's a forward reference error, triggered in this case by CTFE.
------------
class Base6900
{
 void foo() {}
}
class Derived6900: Base6900
{
 override void foo() { }
}
int test6900()
{
 Derived6900 d = new Derived6900; // for github HEAD
 // Derived6900 d = null; // for older versions
 d.foo();
 return 1;
}
static assert(test6900());
------------
test.d(8): Error: variable test.Derived6900.foo.this override cannot be applied
to variable
test.d(15): called from here: d.foo()
test.d(19): called from here: test6900()
test.d(19): Error: static assert (test6900()) is not evaluatable at compile tim
e

https://github.com/D-Programming-Language/dmd/commit/366a1d759ed45d2aa4bfcb431a0d1ded1f8cf0fc
https://github.com/D-Programming-Language/dmd/commit/a25c281637a5cfdfad7eb55487ebfffca8bd49df