Remove annoying warnings about using a deprecated extension
when compiling via gcc-3.0.

#if __GNUC__ >= 3
/* Assume that a flexible array member at the end of a struct
 * can be defined thus: T arr[]; */
#define FLEXIBLE_ARRAY
#else
/* Assume that it must be defined thus: T arr[0]; */
#define FLEXIBLE_ARRAY 0
#endif

A test program (hsking) compiled fine with gcc-3.0!