Allow postfix ops on vector-dereferenced values

[elimirks]

The following test case will fail on the final two asserts:

test_dereferenced() {
    printf("Testing dereferencing a vec while accessing an element*n");
    auto as[4] 1, 2, 3, 4, 5;
    auto ptr;
    ptr = &as;

    assert_eq_int(as[0], **ptr);
    assert_eq_int(as[0], *ptr[0]);
    assert_eq_int(as[2], *ptr[2]);

    assert_eq_int(3, as[2]);
    *ptr[2] =+ 1;
    assert_eq_int(4, as[2]);
    as[2]++;
    assert_eq_int(5, as[2]);
    (*ptr)[2]++;
    assert_eq_int(6, as[2]);
}

It complains that Compile error: ++ or -- must operate on a memory location.