Assume 'epic5-1.1.2'
http://www.epicsol.org/
# yum provides */iconv ( The reply was = glibc-common-2.13-1.x86_64 )
# yum install glibc-devel
( You will not have a usable gcc without glibc-devel.)
May be you are missing all the development tools ?
→ → # yum groupinstall "Development Tools"
Other dependencies for epic5 : # yum install perl-ExtUtils-Embed
..