> static synchronized int foo;

In fact, applying `synchronized` for variable declaration does not make errors with 2.062 and git head.
```d
static synchronized int foo;   // compiles OK
class C {
    static synchronized int foo;   // compiles OK
}
```

Because, STCsynchronized is explicitly sikkped at the beginning of `VarDeclaration::semantic`.
```cpp
    /* Pick up storage classes from context, but skip synchronized
     */
    storage_class |= (sc->stc & ~STCsynchronized);
```

So, this change just disables errors caused by applying `override`/`abstract`/`final` for `static` and `enum` declarations.