Which version of Core are you using?
If on x86 below tc7.x then download and load libiconv.tcz .
wget -P /etc/sysconfig/tcedir/optional http://tinycorelinux.net/5.x/x86/tcz/libiconv.tcz
tce-load -i libiconv.tcz
Just make sure you don't have it loaded when compiling anything.