if detected, WITH_ICONV will be defined in the C code
WITH_ICONV is also added to Makefile.config
OSX do not use this flag setting in Makefile.config, as it is set at compile time based on target OS version
the actual C code is not changed as the current iconv code is hardcoded for OSX and would break if any other OS got iconv
This detection system is by request of Darkvater