Fix for building on non Win32

src/multimon.cpp

@@ -19,14 +19,13 @@
    Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
  */
 
+#if defined(GDEF_OS_WINDOWS)
+
 #include "multimon.h"
-
 #include "debugging/debugging.h"
-
 #include "gtkutil/window.h"
 #include "preferences.h"
 
-
 multimon_globals_t g_multimon_globals;
 
 LatchedValue<bool> g_Multimon_enableSysMenuPopups(false, "Floating windows sysmenu icons");
@@ -102,3 +101,4 @@ void MultiMon_Construct()
 void MultiMon_Destroy()
 {
 }
+#endif