Make sure that 'libardour-config,h' only gets #included when building with waf (as it only gets generated when building with waf)

When building with MSVC this was getting #included in a few places which had the effect of making my session files get generated in a very old format.

libs/ardour/ardour/port.h

@@ -20,7 +20,9 @@
 #ifndef __ardour_port_h__
 #define __ardour_port_h__
 
+#ifdef WAF_BUILD
 #include "libardour-config.h"
+#endif
 
 #include <set>
 #include <string>

libs/ardour/ardour/session.h

@@ -20,7 +20,9 @@
 #ifndef __ardour_session_h__
 #define __ardour_session_h__
 
+#ifdef WAF_BUILD
 #include "libardour-config.h"
+#endif
 
 #include <exception>
 #include <list>

libs/ardour/lv2_plugin.cc

@@ -45,7 +45,9 @@
 #include "pbd/windows_special_dirs.h"
 #endif
 
+#ifdef WAF_BUILD
 #include "libardour-config.h"
+#endif
 
 #include "ardour/audio_buffer.h"
 #include "ardour/audioengine.h"