($os alternatives for sco and isc): Preserve the specified os version if any.

($os alternatives for sco and isc): Preserve the specified os version if any.

Each alternative handles both 386 and 486, preserving distinction.
($basic_machine alternatives for sco and isc): Deleted.
(i[34]86v32, i[34]86v, i[34]86v4):
Handle both cpus together, preserving distinction.

From-SVN: r3093