[plugin] fix load struct

[yuxiaomao]

Fix "Imported type 'SharedStruct' could not be resolved".

Repro: run with haxe build.hxml && haxe plugin.hxml && hl test.hl

// Main.hx
class Main {
	static function main() {
		hl.Api.loadPlugin("plugin.hl");
	}
}

@:struct
class SharedStruct {
	public var value:Int;
	public var name:String;
	public function new(value:Int, name:String) {
		this.value = value;
		this.name = name;
	}
	public function sum(v:Int):Int {
		return value + v;
	}
}

// Plugin.hx
class Plugin {
	static function main() {
		struct_resolve();
	}
	static function struct_resolve() {
		var s = new Main.SharedStruct(10, "hello");
		eq(s.value, 10);
		t(Std.isOfType(s, Main.SharedStruct));
	}
	static inline function eq<T>(actual:T, expected:T, ?infos:haxe.PosInfos) {
		if (actual != expected)
			haxe.Log.trace('FAIL: $actual, expected=$expected', infos);
		else
			haxe.Log.trace('OK: $actual', infos);
	}
	static inline function t(actual:Bool) {
		eq(actual, true);
	}
}

// build.hxml
--main Main
-D hl-check
--hl test.hl

// Plugin.hxml
-hl plugin.hl
-main Plugin
--macro exclude("SharedStruct")