gh-149879: Set thread name max length on Cygwin (#149890)

This change fix test_threading on Cygwin.

Author: vstinner

configure

@@ -7850,6 +7850,7 @@ case "$ac_sys_system" in
   iOS) _PYTHREAD_NAME_MAXLEN=63;;
   FreeBSD*) _PYTHREAD_NAME_MAXLEN=19;; # gh-131268
   OpenBSD*) _PYTHREAD_NAME_MAXLEN=23;; # gh-131268
+  CYGWIN*) _PYTHREAD_NAME_MAXLEN=16;;
   *) _PYTHREAD_NAME_MAXLEN=;;
 esac
 if test -n "$_PYTHREAD_NAME_MAXLEN"; then