Add function getpeereid.

(backport <#4524>)
(cherry picked from commit 336e3f1)

Author: Xing Xue

libc-test/build.rs

@@ -5729,6 +5729,9 @@ fn test_aix(target: &str) {
             // https://github.com/gnzlbg/ctest/issues/68.
             "lio_listio" => true,
 
+            // The function is only available under macro _KERNEL in 'proto_uipc.h'.
+            "getpeereid" => true,
+
             _ => false,
         }
     });

libc-test/semver/aix.txt

@@ -1989,6 +1989,7 @@ getmntent
 getnameinfo
 getopt
 getpagesize
+getpeereid
 getpeername
 getpgid
 getpgrp

src/unix/aix/mod.rs

@@ -2949,6 +2949,7 @@ extern "C" {
         flags: c_int,
     ) -> c_int;
     pub fn getpagesize() -> c_int;
+    pub fn getpeereid(socket: c_int, euid: *mut crate::uid_t, egid: *mut crate::gid_t) -> c_int;
     pub fn getpriority(which: c_int, who: crate::id_t) -> c_int;
     pub fn getpwent() -> *mut crate::passwd;
     #[link_name = "_posix_getpwnam_r"]