watchman @3.1: builds with datatype mismatch in clang

[siulung@…]

$ sudo port install watchman
--->  Computing dependencies for watchman
--->  Fetching archive for watchman
--->  Attempting to fetch watchman-3.1_0+universal.darwin_14.i386-x86_64.tbz2 from http://packages.macports.org/watchman
[...]
Error: org.macports.build for port watchman returned: command execution failed
Please see the log file for port watchman for details:
    /opt/local/var/macports/logs/_opt_local_var_macports_sources_rsync.macports.org_release_tarballs_ports_sysutils_watchman/watchman/main.log

:info:build watcher/fsevents.c:133:67: error: values of type 'FSEventStreamEventFlags' should not be used as format arguments; add an explicit cast to 'unsigned int' instead [-Werror,-Wformat]
:info:build     w_log(W_LOG_DBG, "fse_thread: add %s %" PRIx32 "\n", pathbuf, evt->flags);
:info:build                                          ~~~                      ^~~~~~~~~~
:info:build                                                                   (unsigned int)
:info:build 1 error generated.