libiconv for windres

[Danny Smith]

> 
> That's right. I introduced the API needed for the 
> windmc-tool. But also I 
> think the missing "-c" option can be implemented by this methods to 
> windres, too.
> 
> Cheers,
>  i.A. Kai Tietz

I think I finally see where you are going now.
A few more comments in your code would be nice.

This still needs to be fixed:

cc1.exe: warnings being treated as errors
../../src/binutils/winduni.c: In function 'wind_MultiByteToWideChar':
../../src/binutils/winduni.c:636: warning: unused variable 'used_def'
make[4]: *** [winduni.o] Error 1


Otherwise, I have no objection to your patch (but, to be clear, I so not have authoirity to approve).
I see no regressions in the windres testsuite on mingw32,

Thanks
Danny