LibGC: Enable EXPLICIT_SYMBOL_EXPORT

Author: https://github.com/ayeteadoe
Commit: 83846b3861
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/5215
Reviewed-by: https://github.com/ADKaster ✅

Libraries/LibGC/Forward.h

@@ -7,6 +7,7 @@
 #pragma once
 
 #include <AK/Types.h>
+#include <LibGC/Export.h>
 
 namespace GC {