Fix Windows builds

This fixes a missing symbol error due to the weird way how
Windows maps the same, identical symbols using different addresses
in .dll and .exe.  Here specifically for

int luabridge::CFunc::vectorToArray<double, std::vector<double, std::allocator<double> > >(lua_State*)

which was added in 5e1a73a28c07 resulting in

gtk2_ardour/luainstance.cc error: explicit instantiation of 'static const void* luabridge::ClassInfo<T>::getStaticKey() [with T = std::vector<double>]' but no definition available [-fpermissive]
gtk2_ardour/luainstance.cc error: explicit instantiation of 'static const void* luabridge::ClassInfo<T>::getClassKey() [with T = std::vector<double>]' but no definition available [-fpermissive]
gtk2_ardour/luainstance.cc error: explicit instantiation of 'static const void* luabridge::ClassInfo<T>::getConstKey() [with T = std::vector<double>]' but no definition available [-fpermissive]

1 files changed, 30 insertions, 0 deletions

diff --git a/gtk2_ardour/luainstance.cc b/gtk2_ardour/luainstance.cc
index fa858888a3..12c474229e 100644
--- a/gtk2_ardour/luainstance.cc
+++ b/gtk2_ardour/luainstance.cc
@@ -62,6 +62,36 @@
 
 static const char* ui_scripts_file_name = "ui_scripts";
 
+#ifdef PLATFORM_WINDOWS
+/* see libs/ardour/luabindings.cc for details */
+
+template <class T>
+void const*
+luabridge::ClassInfo<T>::getStaticKey ()
+{
+	static char value;
+	return &value;
+}
+
+template <class T>
+void const*
+luabridge::ClassInfo<T>::getClassKey ()
+{
+	static char value;
+	return &value;
+}
+
+template <class T>
+void const*
+luabridge::ClassInfo<T>::getConstKey ()
+{
+	static char value;
+	return &value;
+}
+
+CLASSKEYS(std::vector<double>);
+#endif
+
 namespace LuaCairo {
 /** wrap RefPtr< Cairo::ImageSurface >
  *