This commit adds the DirectSound audio backend, which is a modified
version of core/oslib/ds_audiostream.cpp.
Porting this was a bit tricky, since ds_audiostream.cpp defined 3
extern functions that the other backends didn't have:
* bool os_IsAudioBuffered();
* bool os_IsAudioBufferedLots();
* int os_getusedSamples();
I came to the conclusion that these methods are obsolete since they are
only used core/windows/winmain.cpp in the function void os_wait_cycl(u32
cycl) - which is used nowhere. Thus, I removed os_wait_cycl and the
headers of the three functions in core/oslib/oslib.h. I also removed the
functions themselves (except for int os_getusedSamples(), which is still
used inside the directsound backend, but can safely declared static for
that purpose).
The DirectSound backend will be included during compilation if HOST_OS
is OS_WINDOWS.
Jan Holthuis