unistd.h: fix wrong type for gid_t argument

the prototype is defined with const gid_t* rather than const gid_t[].
it was already correctly defined in grp.h.

include/unistd.h

@@ -168,7 +168,7 @@ int getdtablesize(void);
 int sethostname(const char *, size_t);
 int getdomainname(char *, size_t);
 int setdomainname(const char *, size_t);
-int setgroups(size_t, const gid_t []);
+int setgroups(size_t, const gid_t *);
 char *getpass(const char *);
 int daemon(int, int);
 void setusershell(void);