The platform specific tweaking part was using 'uname -o' which
is not always available. Squelch error message from it.
It was suggested to chain the if..else, but I chose not to, because
maintaining the nested if..else if..else..endif endif to match is a
pain. If we had "elif", things would have been different, though.
While we are at it, try not to invoke 'uname -s' for each platform
candidate.