os2: integrate the port into main tree.

src/events/SDL_mouse.c

@@ -32,6 +32,10 @@
 #ifdef __WIN32__
 #include "../core/windows/SDL_windows.h"    // For GetDoubleClickTime()
 #endif
+#if defined(__OS2__)
+#define INCL_WIN
+#include <os2.h>
+#endif
 
 /* #define DEBUG_MOUSE */
 
@@ -54,6 +58,8 @@ SDL_MouseDoubleClickTimeChanged(void *userdata, const char *name, const char *ol
     } else {
 #ifdef __WIN32__
         mouse->double_click_time = GetDoubleClickTime();
+#elif defined(__OS2__)
+        mouse->double_click_time = WinQuerySysValue(HWND_DESKTOP, SV_DBLCLKTIME);
 #else
         mouse->double_click_time = 500;
 #endif