This is the very first step for merging the `mmdevdrv.c` files into a single one.
The commit strictly focuses on Linux drivers, `wine{oss,coreaudio}` will follow.
Huge thanks to @jacek and @huw for making this simple, as they took care of ELF/PE separation.
-- v2: wine{alsa,pulse}: Merge unixlib.h, move it into mmdevapi