Status output related to OBS configuration is prefixed with the string
"OBS" and added padding for enabled and disabled features. This padding
was not aligned between platforms.
By moving the padding and prefix decoration into its own function,
both elements are controlled in a single place. CMake scripts were
changed to use this new function `obs_status` instead of using CMake's
`message` function directly.
This implements OSS audio input capturing support for OSS-capable OSes.
FreeBSD and DragonFly (not yet tested on) supports are added as a
starting point.
