It is convenient to assume that everybody who wants to build & test Git
has access to a working `iconv` executable (after all, we already pretty
much require libiconv).
However, that limits esoteric test scenarios such as Git for Windows',
where an end user installation has to ship with `iconv` for the sole
purpose of being testable. That payload serves no other purpose.
So let's just have a test helper (to be able to test Git, the test
helpers have to be available, after all) to act as `iconv` replacement.
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
3e4400fb83