restorer: Add "memory" constraint into asm statement

It seems otherwise older gcc compilers do treat this
statement as incomplete.
Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
Reported-by: Huang Qiang <h.huangqiang@huawei.com>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>

restorer.c

@@ -705,6 +705,6 @@ core_restore_failed:
 		"jmp *%%rax				\n"
 		:
 		: "r"(ret)
-		: );
+		: "memory");
 	return ret;
 }