*** NOTE: this has to be synced with SR#959809 ***

- Disable the build of example-tools which are now built in a
separate jack-example-tools package.
- update to 1.9.20:
* Add waf autooption --example-tools to allow optional build of
executables, libraries and man pages provided by
jack-example-tools (the files are built by default). Building
and installing the additional files can be disabled by using
--example-tools=no or --no-example-tools.
* Fix 32-bit support in ALSA driver
* Fix incomplete ASIO support on Windows
* Fix metadata usage with multiple users
* Fix netsource tool missing on Windows
* Fix semaphore usage on macOS
* Official FreeBSD support