2013/11/10 Eli Zaretskii <eliz@gnu.org>
> Date: Sun, 10 Nov 2013 10:16:51 +0100
> From: Panicz Maciej Godek <godek.maciek@gmail.com>
> Cc: "guile-user@gnu.org" <guile-user@gnu.org>
>
> The dependency walker shows that libiconv depends only on dlls supplied
> by Windows (kernel32.dll, msvcrt.dll and ntdll.dll). The dependency on
> libgcc appears only in libguile, but it seems to have nothing to do with
> iconv. Rebuilding libiconv didn't change anything

Then I guess you will have to run that compilation under GDB and see
why it thinks utf8 is invalid encoding.  (Is it really "utf8" or
"utf-8" or maybe "UTF-8"?)

Well, I think that is the reason of the problem -- that for some reason
Windows reports "utf8" encoding, while iconv requires it to be "UTF-8".
If I only knew where exactly is the encoding set to "utf8", I could try
to fix that. (I think that the problem appears only with applications
compiled with -mwindows flag).
However, it turned out that this problem is only superficial -- it appears
when Guile is trying to print backtrace caused by other problems resulting
from the differences in the execution environment (lack of certan libraries,
mostly).
Although it would be helpful to have more feedback from the interpreter,
I think that I should manage to provide all the necessary fixes without it.