x86: don't call wait4 as waitpid

Fix compilation on ARM:
pie/restorer.c: In function ‘wait_helpers’:
pie/restorer.c:728:3: error: implicit declaration of function ‘sys_waitpid’ [-Werror=implicit-function-declaration]
cc1: all warnings being treated as errors

Reported-by: Mr Jenkins
Signed-off-by: Andrey Vagin <avagin@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>

arch/x86/syscall-x86-64.def

@@ -43,7 +43,7 @@ __NR_setsockopt		54		sys_setsockopt		(int sockfd, int level, int optname, const
 __NR_getsockopt		55		sys_getsockopt		(int sockfd, int level, int optname, const void *optval, socklen_t *optlen)
 __NR_clone		56		sys_clone		(unsigned long flags, void *child_stack, void *parent_tid, void *child_tid)
 __NR_exit		60		sys_exit		(unsigned long error_code)
-__NR_wait4		61		sys_waitpid		(int pid, int *status, int options, struct rusage *ru)
+__NR_wait4		61		sys_wait4		(int pid, int *status, int options, struct rusage *ru)
 __NR_kill		62		sys_kill		(long pid, int sig)
 __NR_fcntl		72		sys_fcntl		(int fd, int type, long arg)
 __NR_flock		73		sys_flock		(int fd, unsigned long cmd)

pie/restorer.c

@@ -725,7 +725,7 @@ static int wait_helpers(struct task_restore_args *task_args)
 		pid_t pid = task_args->helpers[i];
 
 		/* Check that a helper completed. */
-		if (sys_waitpid(pid, &status, 0, NULL) == -1) {
+		if (sys_wait4(pid, &status, 0, NULL) == -1) {
 			/* It has been waited in sigchld_handler */
 			continue;
 		}