Hoist the code for checking whether or not iconv actually works up into the

Hoist the code for checking whether or not iconv actually works up into the
loop that looks for iconv, because we might have more than one version
of iconv available and the first version might not work like we want, so
we have to keep looking.

We have yet to look for other character conversions as well, but for now,
let's see what the build farm makes of the changes.
(This used to be commit 13be2ca51a6125a6de22fa7afb88ba0688f23ab8)