The following shall be declared as functions and may also be defined
as macros. Function prototypes shall be provided.
struct group *getgrgid(gid_t);
struct group *getgrnam(const char *);
int getgrgid_r(gid_t, struct group *, char *,
size_t, struct group **);
int getgrnam_r(const char *, struct group *, char *,
size_t , struct group **);
struct group *getgrent(void);
void endgrent(void);
void setgrent(void);