I don't know this application at all. But from what you've posted here
- Their configure tool does not find iconv, even though it is installed.
- Their configure tool does not perceive iconv to be a dependency, even though it apparently is one.
The httrack application developers may want to know #2. They may see #1 as your responsibility, as you are attempting to port their application to an operating system they do not support.
For
your consideration:
I will assume that since there are header files, the program source code is written in C, and a gcc(1) or gcc-compatible compiler is used. That compiler uses the -I option to add directories to the header file search.
Perhaps the configure tool has an option to add compiler options and flags? These configure tools are usually shell scripts. Take a look through it, and see what the tool allows you to specify.