sim65: S_IREAD and S_IWRITE are nonstandard.

sim65: S_IREAD and S_IWRITE are nonstandard.

The Linux build was failing with:

sim65/paravirt.c: In function ‘PVOpen’:
sim65/paravirt.c:217:18: error: ‘S_IREAD’ undeclared (first use in this function)
         OMode |= S_IREAD;
                  ^
sim65/paravirt.c:217:18: note: each undeclared identifier is reported only once for each function it appears in
sim65/paravirt.c:220:18: error: ‘S_IWRITE’ undeclared (first use in this function)
         OMode |= S_IWRITE;
                  ^
make[1]: *** [../wrk/sim65/paravirt.o] Error 1