Log Message:
Update to msmtp-1.4.5.  This addresses PR/32517.  Notable changes include:
- gnulib update.
- adapted configure.ac for new pkg-config version
- Use gnulib socklen module for socklen_t.
- Lock the logfile.
- W32/DJGPP: Use all files/streams in binary mode.
- W32: Allow %HOME% to override default user configuration directory.
- W32: Enable getpass and netrc functionality.
- Use gnulib getpass module since it now works on Win32.
- Shut down a GnuTLS TLS session with GNUTLS_SHUT_WR instead of
  GNUTLS_SHUT_RDWR. This prevents session hangs in certain situations.
  It is safe to do this because we never reuse a connection when TLS was shut
  down. Thanks to Jens Kammler for the problem report!
- Do not rely on a failing malloc setting errno in xalloc_die()
- Make the GnuTLS code accept old version 1 CA certificates when verifying
  certificates.
- Renamed LOCK_(READ|WRITE) to OSENV_LOCK_(READ|WRITE) in os_env.[ch] to avoid
  name clashes with <fcntl.h>