libao is missing some symbols (ao_file_extension)
The libao package is missing some symbols. Those should be added/patched
in the version 1.2 but are not included on Alpine.
Found out about this while trying to run an example of the Lua binding, details at https://github.com/TheLinx/lao/issues/9
(from redmine: issue id 8044, created on 2017-10-24)