It was kind of ugly to have this kind of special flag directly in
link.od; now we detect whether it's available. This also gives a
project the ability to override the flag in some other way if they
want.
As a result, rc/shlib.rc needs to be included in all.rc.od if you want
to create or link against shared libraries.
While we're here, also add -Wl,-z,origin on platforms where it works.
This is apparently needed for FreeBSD 8.0 at least, and probably other
platforms.
Reported-by: Wayne Scott <wsc9tt@gmail.com>
88250334da