What's new:
-----------

- Revamped pseudo console support.

- New C11 threads API: call_once, cnd_broadcast, cnd_destroy, cnd_init,
  cnd_signal, cnd_timedwait, cnd_wait, mtx_destroy, mtx_init, mtx_lock,
  mtx_timedlock, mtx_trylock, mtx_unlock, thrd_create, thrd_current,
  thrd_detach, thrd_equal, thrd_exit, thrd_join, thrd_sleep, thrd_yield,
  tss_create, tss_delete, tss_get, tss_set.


What changed:
-------------

- Allow ~5000 child processes per process on 64 bit, ~1200 child processes
  per process on 32 bit.  So far, only 256 child processes per process were
  supported.

- A few FAQ updates.


Bug Fixes
---------

- Iterate at least 4 times over pthread_key_t destructors per POSIX.

- The pthread_yield declaration in pthread is now visible by default
  or when defining _BSD_SOURCE, too.

- Fix SEGV in modfl call.
  Addresses: https://cygwin.com/pipermail/cygwin/2020-August/246056.html

- Fix a collision of offical and internally used file flags.
  Addresses: https://cygwin.com/pipermail/cygwin/2020-September/246174.html

- Fix assertion failure on an invalid path under /proc/<pid>/fd/.
  Addresses: https://cygwin.com/pipermail/cygwin/2020-September/246160.html

- Fix crash on stat(2)'ing /dev/ptmx on 32 bit.
  Addresses: https://cygwin.com/pipermail/cygwin/2020-September/246218.html

- Fix return value of sqrtl on negative infinity.
  Addresses: https://cygwin.com/pipermail/cygwin/2020-October/246606.html

- Fix a path handling problem if there is a WSL symlink in PATH.
  Addresses: https://cygwin.com/pipermail/cygwin/2020-December/246938.html

- Fix a bug in fstatat(2) on 32 bit that could cause it to return garbage.
  Addresses: https://cygwin.com/pipermail/cygwin/2021-January/247399.html

- Fix the errno when a path contains .. and the prefix exists but is
  not a directory.
  Addresses: https://lists.gnu.org/archive/html/bug-gnulib/2021-01/msg00214.html

- Fix the return value when ptsname_r(3) is called with a bad file descriptor
  Addresses: https://lists.gnu.org/archive/html/bug-gnulib/2021-01/msg00245.html