Does getopt() return "-1", or "EOF", at end?

I notice that in some places we compare the result of getopt(3) to
"EOF", and in some other places we compare it to "-1".  I think we
should standardize on one or the other; anyone have an opinion
which it should be?

The man pages I have here (HPUX and Linux) both describe the
end-of-switches return value as being "-1".  The glibc sources also
use "-1".  Replacing this by EOF seems more readable but perhaps is
not strictly correct.

Are there any platforms that define EOF as something other than -1?
        regards, tom lane