cargo can't resolve iconv under macports libiconv 1.16

Nobody has claimed this yet.

To build pyoxidixer, apparently I need to resolve references from libiconv

The error message under compilation suggests it's using -liconv so it knows to look for this library.

I can't use homebrew on this system. I have libiconv 1.16, which is the latest, from macports

tmp andrew.philpot$ sudo port list libiconv
libiconv @1.16 textproc/libiconv

This appears to have installed into
/opt/local/lib/libiconv.2.dylib
/opt/local/lib/libiconv.dylib
/opt/local/lib/libiconv.a

as well there seems to be a set of libs in
/usr/lib/libiconv.2.4.0.dylib
/usr/lib/libiconv.2.dylib
/usr/lib/libiconv.dylib

For open SSL I was able to set a global but I don't see any way described for this dependency. I'm supposing there is a way to indicate this lib location in one of the build inputs but don't know where to start.

Logically, one might think this is a rust/cargo internals issue, but the backtrace seems to point more directly at pyoxidizer, which is why I am posting here first.

[pyoxidizer-compile.stderr.txt](https://github.com/indygreg/PyOxidizer/files/3627479/pyoxidizer-compile.stderr.txt)

Start by reading the attached pyoxidizer-compile.stderr.txt and the issue's description of the Cargo build on macOS with MacPorts libiconv 1.16. Trace where PyOxidizer's build inputs resolve the -liconv reference. Done means the reported configuration can build pyoxidizer using the MacPorts library without requiring Homebrew.

Written by the indexing model from the issue text.