Ship a fallback natupnp.h

MinGW doesn't bring a natupnp.h out of the box. Add one to the repository
so MinGW builds also support UPnP/NAT-PMP.

CMakeLists.txt

@@ -742,6 +742,10 @@ if(USE_CONSOLE)
 	CHECK_INCLUDE_FILE_CXX(readline/readline.h HAVE_READLINE_READLINE_H)
 endif()
 CHECK_INCLUDE_FILE_CXX(natupnp.h HAVE_NATUPNP_H)
+if(NOT HAVE_NATUPNP_H)
+	include_directories(thirdparty/natupnp)
+	set(HAVE_NATUPNP_H TRUE CACHE BOOL "natupnp.h available" FORCE)
+endif()
 CHECK_INCLUDE_FILES_CXX("X11/Xlib.h;X11/extensions/Xrandr.h" HAVE_X11_EXTENSIONS_XRANDR_H)
 CHECK_INCLUDE_FILES_CXX("X11/Xlib.h;X11/keysym.h" HAVE_X11_KEYSYM_H)
 

src/network/C4Network2UPnPWin32.cpp

@@ -20,7 +20,17 @@
 #include "C4Version.h"
 
 #include <boost/foreach.hpp>
+
+#ifdef __GNUC__
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wnon-virtual-dtor"
+#pragma GCC diagnostic ignored "-Wredundant-decls"
+#pragma GCC diagnostic ignored "-Wunknown-pragmas"
+#endif
 #include <natupnp.h>
+#ifdef __GNUC__
+#pragma GCC diagnostic pop
+#endif
 
 #if defined(__MINGW32__) || defined(__MINGW64__)
 // MinGW doesn't usually have these