Native Libraries:

- made C methods `static` (similar to `private` in Java) to avoid that they are added (exported) to shared library symbol table
- macOS and Linux: added `-fvisibility=hidden` to compiler options to mark C methods hidden by default

flatlaf-natives/flatlaf-natives-windows/src/main/cpp/WinWrapper.cpp

@@ -25,8 +25,8 @@
  * @author Karl Tauber
  */
 
-// see FlatWndProc.cpp
-HWND getWindowHandle( JNIEnv* env, jobject window );
+// declare external methods
+extern HWND getWindowHandle( JNIEnv* env, jobject window );
 
 //---- Utility ----------------------------------------------------------------