include libiconv on linux

[jjhelmus]

Include libiconv in the host requirements on linux.

Alternatively the libiconv implementation included with glibc could be used but getting ./configure to ignore the stand alone version pulled in by libxml2 seems difficult. It seem as if --without-libiconv-prefix could be used but in tests that argument did not work.

closes #35

Checklist

• [x] Used a fork of the feedstock to propose changes
• [x] Bumped the build number (if the version is unchanged)
• [ ] Reset the build number to 0 (if the version changed)
• [x] Re-rendered with the latest conda-smithy (Use the phrase code>@<space/conda-forge-admin, please rerender in a comment in this PR for automated rerendering)
• [x] Ensured the license file is being packaged.

[conda-forge-linter]

Hi! This is the friendly automated conda-forge-linting service.

I just wanted to let you know that I linted all conda-recipes in your PR (recipe) and found it was in an excellent condition.

[jjhelmus]

@conda-forge-admin, please rerender

[epignatelli]

Since the packages are broken already, no conda install or conda update call woks.

What's the process to update the package and fix https://github.com/conda/conda/issues/8838 for ubuntu 16.04?

[epignatelli]

A solution for me has been: https://github.com/conda/conda/issues/8838#issuecomment-513200854