https://github.com/audacity/audacity/issues/4614

When compile w/ clang, link failed with:

  ld.lld: error: undefined symbol: typeinfo for wxNavigationEnabled<wxWindow>

so disable "extern ..." if compiler is clang

see also gentoo bug: https://bugs.gentoo.org/915041

diff --git a/src/ListNavigationPanel.h b/src/ListNavigationPanel.h
index 1618d78..e04cc23 100644
--- a/src/ListNavigationPanel.h
+++ b/src/ListNavigationPanel.h
@@ -13,7 +13,9 @@
 #include <wx/window.h>
 #include <wx/containr.h>
 
+#if !defined(__clang__)
 extern template class WXDLLIMPEXP_CORE wxNavigationEnabled<wxWindow>;
+#endif
 
 #include "ListNavigationEnabled.h"