See https://github.com/android/ndk/issues/533

--- a/libs/ardour/ardour/port_engine.h
+++ b/libs/ardour/ardour/port_engine.h
@@ -78,7 +78,7 @@
 class LIBARDOUR_API ProtoPort {
   public:
 	ProtoPort() {}
-	virtual ~ProtoPort () {}
+	virtual ~ProtoPort ();
 };
 
 class LIBARDOUR_API PortEngine
--- a/libs/ardour/port_engine.cc
+++ b/libs/ardour/port_engine.cc
@@ -0,0 +1,3 @@
+#include "ardour/port_engine.h"
+using namespace ARDOUR;
+ProtoPort::~ProtoPort() {}
--- a/libs/ardour/wscript
+++ b/libs/ardour/wscript
@@ -186,6 +186,7 @@
         'plugin_scan_result.cc',
         'polarity_processor.cc',
         'port.cc',
+        'port_engine.cc',
         'port_engine_shared.cc',
         'port_insert.cc',
         'port_manager.cc',