syscalls: Add getgroups syscall

Getting groups can be done vie proc, but there's only 32 on them,
while task may have up to 65k :( We will use parasite for that and
thus require this syscall definition.
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>

include/syscall-x86-64.def

@@ -44,6 +44,7 @@ __NR_mkdir		83		sys_mkdir		(const char *name, int mode)
 __NR_rmdir		84		sys_rmdir		(const char *name)
 __NR_unlink		87		sys_unlink		(char *pathname)
 __NR_readlink		89		sys_readlink		(const char *path, char *buf, int bufsize)
+__NR_getgroups		115		sys_getgroups		(int gsize, unsigned int *groups)
 __NR_setresuid		117		sys_setresuid		(int uid, int euid, int suid)
 __NR_setresgid		119		sys_setresgid		(int gid, int egid, int sgid)
 __NR_getpgid		121		sys_getpgid		(void)