archcheck looks for dylibs even on non OS X operating systems

[rudloff@…]

--->  Configuring gettext
Error: The file /opt/local/lib/libiconv.dylib does not exist, though it was
Error: expected to have been provided by one of gettext's dependencies. Try
Error: rebuilding the port that should have provided that file by running
Error: 
Error:     sudo port -n upgrade --force <portname>
Error: 
Error: Target org.macports.configure returned: missing required file

The archcheck should probably look for libiconv.so on Linux.

[ryandesign@…]

This problem is generic to most ports that use the archcheck portgroup. (Any port using archcheck that checks libraries, as opposed to programs.) The archcheck portgroup is for dealing with the problem that OS X has run on four different processor architectures, and sometimes users migrate between them, and some things break. My assumption is that on other operating systems, everything would break if you attempted to do that. So I'll just make the archcheck portgroup only run on OS X, since on other OSes you'd probably fail way before you ever got to running MacPorts itself.

[ryandesign@…]

r88030.