shairport-sync: Update to version 3.3.8

shairport-sync: Update to version 3.3.8

- Update from 3.3.7 to 3.3.8
- Update of rootfile not required
- Changelog
   Version 3.3.8
     **Enhancements**
       * Documentation for the MQTT interface. Many thanks to [minix1234](https://github.com/minix1234)!
     **Bug Fixes**
       * Fix a bug in the `alsa` back end. In the interval between checking that the alsa
         device handle was non-`NULL` and actually using it, the handle could be set to
         `NULL`. The interval between check and usage is now protected.
       * Fix a bug in the `alsa` precision timing code. Thanks to
         [durwin99](https://github.com/durwin99),
         [Nicolas Da Mutten](https://github.com/cleverer),
         [mistakenideas](https://github.com/mistakenideas),
         [Ben Willmore](https://github.com/ben-willmore) and
         [giggywithit](https://github.com/giggywithit) for the
         [report](https://github.com/mikebrady/shairport-sync/issues/1158).
       * Fix a bug that caused Shairport Sync to hang, but not actually crash, if an
         `on-...` script failed.
       * Fix a crash that occurred if metadata support is enabled during compilation but
         turned off in the configuration file. Thanks to
         [Tim Curtis](https://github.com/moodeaudio) for the report.
       * Fix a crash that occurred playing from AirPower on Android. Thanks to
         [Ircama](https://github.com/Ircama) for the report.
       * Fix the configure.ac file so that `--without-<feature>` configuration options
         are not interpreted as `--with-<feature>` options instead! Thanks to
         [David Racine](https://github.com/bassdr) for the report.

Signed-off-by: Adolf Belka <adolf.belka@ipfire.org>
Signed-off-by: Arne Fitzenreiter <arne_f@ipfire.org>