-- errno.h is required for 'errno';
-- don't use str(n)casecmp and rely on ZDoom CMake handling;
-- add a missing parenthesis around a 'signed char' cast;
-- remove an unneeded GNU_SOURCE redefinition;
-- the non-MSVC side of snd_mididevice was not adapted to the new code, making wildmidi unavailable through the menu.
- Besides being little-endian centric, this bit shifting madness
was unneccessary since the values were already clamped to a 16-bit
range, so all we need to do is cast them to a short.
- In order to use ZDoom's own MIDI sequencer event handling must be
completely separate from mixing, but WildMidi had them intertwined
because it wasn't designed for external sequencers.
- Also remove all 'long's defining the output buffers to avoid having
something that's 32 bits wide on Windows and 64 bits wide on Linux.
The pointless error message in WildMidi_Shutdown was removed to keep the rest of the code simple and allowing to call this even when the device never was used.
