Nullability check for wait module.

Bugs: b/245972273
Test: adb shell
Change-Id: I407cc592522fc8feda1916d72525d147c9c58711

libc/include/sys/wait.h

diff --git a/libc/include/sys/wait.h b/libc/include/sys/wait.h
index 96974a2..e6fb855 100644
--- a/libc/include/sys/wait.h
+++ b/libc/include/sys/wait.h
@@ -37,9 +37,9 @@
 
 __BEGIN_DECLS
 
-pid_t wait(int* __status);
-pid_t waitpid(pid_t __pid, int* __status, int __options);
-pid_t wait4(pid_t __pid, int* __status, int __options, struct rusage* __rusage) __INTRODUCED_IN(18);
+pid_t wait(int* _Nullable __status);
+pid_t waitpid(pid_t __pid, int* _Nullable __status, int __options);
+pid_t wait4(pid_t __pid, int* _Nullable __status, int __options, struct rusage* _Nullable __rusage) __INTRODUCED_IN(18);
 
 /* Posix states that idtype_t should be an enumeration type, but
  * the kernel headers define P_ALL, P_PID and P_PGID as constant macros
@@ -47,6 +47,6 @@
  */
 typedef int idtype_t;
 
-int waitid(idtype_t __type, id_t __id, siginfo_t* __info, int __options);
+int waitid(idtype_t __type, id_t __id, siginfo_t* _Nullable __info, int __options);
 
 __END_DECLS