add SIG_ERR definition

// callback value (sa_sigaction of sa_handler) to restore default handling

#define SIG_DFL		((void*)-1)

#define SIG_DFL		((void(*)(int))0)

// callback value (sa_sigaction of sa_handler) ignore signal if possible

#define SIG_IGN		((void*)-3)

#define SIG_IGN		((void(*)(int))-3)

// used as an error value by some functions in user space

#define SIG_ERR		((void(*)(int))-1)

/**