musl: fix test build with musl 1.2.0+

Since musl 1.2.0, the utmpx.ut_session type changed from long to int
(with padding). For now, skip the test for this field.
Fixes: 3305

Author: xbjfk

libc-test/build.rs

@@ -4795,7 +4795,9 @@ fn test_linux(target: &str) {
         (struct_ == "statvfs" && field == "__f_spare") ||
         (struct_ == "statvfs64" && field == "__f_spare") ||
         // the `xsk_tx_metadata_union` field is an anonymous union
-        (struct_ == "xsk_tx_metadata" && field == "xsk_tx_metadata_union")
+        (struct_ == "xsk_tx_metadata" && field == "xsk_tx_metadata_union") ||
+        // FIXME(musl): After musl 1.2.0, the type becomes `int` instead of `long`.
+        (struct_ == "utmpx" && field == "ut_session")
     });
 
     cfg.skip_roundtrip(move |s| match s {