fixed the use of internal OS_WINDOWS in general file libusb.h
fixed the use of internal OS_WINDOWS in general file libusb.h

OS_WINDOWS is only defined in the context of compiling libusb
switched to using the explicit MinGW/cygwin and MS compiler defines

nonolith/libusb,pbatard/libusb-pbatard,pbatard/libusb-pbatard,nonolith/libusb,nonolith/libusb