Add getppid(2)

include/sys/sys_proc.h

@@ -10,6 +10,7 @@ void sys_sigreturn(void);
 int sys_clone(int (*entry) (void *), void *stack, int flags, void *arg);
 int sys_execve(const char *path, const char **argp, const char **envp);
 pid_t sys_getpid(void);
+pid_t sys_getppid(void);
 
 uid_t sys_getuid(void);
 gid_t sys_getgid(void);

include/user/syscall.h

@@ -51,6 +51,7 @@
 #define SYSCALL_NR_SETUID           105
 #define SYSCALL_NR_SETGID           106
 #define SYSCALL_NR_SETPGID          109
+#define SYSCALL_NR_GETPPID          110
 #define SYSCALL_NR_GETPGID          121
 #define SYSCALL_NR_SIGALTSTACK      131
 #define SYSCALL_NRX_WAITPID         247