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
bjarni