This avoids static builds putting the "no-op" implementation of
PlaybackStream::create() in the static archive before the strong
implementation later. On ELF (and probably PE/COFF too), a weak
definition in a static archive is chosen and locked-in as the
definition before a strong definition later in the archive.
Before this change, static builds would have no audio support
at all.
b7f7f58e5f