[WHLSL] Structs should be able to recursively point to each other

[Justin Fan]

This code does not compile but should.

        struct Foo {
            thread Bar* bar;
            int foo;
        }
        struct Bar {
            thread Foo* foo;
            int bar;
        }
        int foo()
        {
            Foo foo;
            Bar bar;
            foo.foo = 564;
            bar.bar = 53;
            return foo.bar->bar - bar.foo->foo;
        }

[Justin Fan]

When fixing this bug, make sure to update whlsl-recursive-structs.html.

[Myles C. Maxfield]

WHLSL is no longer relevant.