adding pid_type enum for Linux.

[ref](https://github.com/torvalds/linux/blob/7cdabafc001202de9984f22c973305f424e0a8b7/include/linux/pid_types.h#L5)

Author: devnexen

libc-test/semver/linux.txt

@@ -4037,6 +4037,7 @@ packet_mreq
 pause
 personality
 pgn_t
+pid_type
 pipe2
 popen
 posix_fadvise

src/unix/linux_like/linux/mod.rs

@@ -90,6 +90,14 @@ e! {
         TPACKET_V2,
         TPACKET_V3,
     }
+
+    pub enum pid_type {
+        PIDTYPE_PID,
+        PIDTYPE_TGID,
+        PIDTYPE_PGID,
+        PIDTYPE_SID,
+        PIDTYPE_MAX,
+    }
 }
 
 s! {