Configure CMake to require the installed backend libraries. This should
help to find build system regressions.
On TravisCI with Linux this requires the ALSA, PulseAudio, PortAudio, OSS
and JACK backend.
On TravisCI with Android cross compile Linux this requires the OpenSL
backend.
On TravisCI with MacOSX this requires the CoreAudio backend.
ON AppVeyor with Windows this requires the WinMM, DSound and MMDevAPI
backend.
Install Ubuntu development packages for PulseAudio, PortAudio, ALSA and
JACK to enable the building of most Linux backends on TravisCI.
Intall Ubuntu development packages for Qt5 to enable `alsoft-config`.
