[cppia] extern static property getter

cpp host code:
```haxe
class Host {
public static function main() {
trace(Test.foo); // bring the class into compilation
cpp.cppia.Host.runFile('bin/script.cppia');
}
}
```

cppia script code:

```haxe
class Script {
static function main() {
trace("Hello from script!");
trace(Test.foo);
}
}
```

and `Test.hx` file for both

```haxe
#if cppia
extern class Test {
static var foo(get, never):Int;
}
#else
class Test {
public static var foo(get, never):Int;
static function get_foo():Int return 42;
}
#end

```

will result in error:

```
Unknown function : Test_obj::get_foo(0)
Error : Unknown global:Test_obj::get_foo
```