Added --enable-old-sdl for compatibility with older versions of SDL, missing some defines

configure.in

@@ -8,6 +8,12 @@ AC_PREFIX_DEFAULT([/usr])
 AC_PROG_LIBTOOL
 AC_PROG_CC
 AC_PROG_CXX
+AC_ARG_ENABLE([old-sdl], [  --enable-old-sdl   Enabled compatibility for older version of SDL, missing some defines],
+	AC_DEFINE([SDL_BUTTON_X1], 6, [Needed for old SDL versions])
+	AC_DEFINE([SDL_BUTTON_X2], 7, [Needed for old SDL versions])
+	AC_DEFINE([SDL_BUTTON_X1MASK], [SDL_BUTTON(SDL_BUTTON_X1)], [Needed for old SDL versions])
+	AC_DEFINE([SDL_BUTTON_X2MASK], [SDL_BUTTON(SDL_BUTTON_X2)], [Needed for old SDL versions])
+)
 AC_SEARCH_LIBS([sqrt], [m], [], AC_MSG_ERROR([Can't LÖVE without C math library]))
 AC_SEARCH_LIBS([SDL_Init], [SDL], [], AC_MSG_ERROR([Can't LÖVE without SDL]))
 AC_SEARCH_LIBS([glLoadIdentity], [GL], [], AC_MSG_ERROR([Can't LÖVE without OpenGL]))