Under CYGWIN the conditional tests in the altairz80_sio.c source file for the
SIMH pseudo device's getHostsFilenamesCmd and resetSIMHInterfaceCmd
functions need to have UNIX_PLATFORM set to 1 - otherwise they do nothing!
With this fix, the HDIR host command from CP/M now displays a list of files
in host system's current directory under CYGWIN.