Added SDL_DEPRECATED #define.

include/begin_code.h

@@ -33,6 +33,14 @@
 #endif
 #define _begin_code_h
 
+#ifndef SDL_DEPRECATED
+#  if (__GNUC__ >= 4)  /* technically, this arrived in gcc 3.1, but oh well. */
+#    define SDL_DEPRECATED __attribute__((deprecated))
+#  else
+#    define SDL_DEPRECATED
+#  endif
+#endif
+
 /* Some compilers use a special export keyword */
 #ifndef DECLSPEC
 # if defined(__WIN32__)