Define EWOULDBLOCK as an alias of EAGAIN for AIX (#2692)

* Define EWOULDBLOCK as an alias of EAGAIN for AIX.

* rename changelog: 2692.fixed.md -> 2692.added.md

---------

Co-authored-by: Steve Lau <stevelauc@outlook.com>

Author: xingxue-ibm

changelog/2692.added.md

@@ -0,0 +1 @@
+Define errno EWOULDBLOCK as an alias of EAGAIN to match the AIX libc definition.

src/errno.rs

@@ -3247,6 +3247,10 @@ mod consts {
         EOPNOTSUPP = libc::EOPNOTSUPP,
     }
 
+    impl Errno {
+        pub const EWOULDBLOCK: Errno = Errno::EAGAIN;
+    }
+
     #[deprecated(
         since = "0.28.0",
         note = "please use `Errno::from_raw()` instead"