\documentclass[a4paper]{refrep}
\usepackage{bold-extra}

\newcommand*{\acronym}[1]{\textsc{#1}}
\newcommand*{\commonpart}{\mbox{$^{\textsf{c}}$}{}}

\usepackage{index}

\makeindex

\newindex{general}{gdx}{gnd}{General Index}

\newcommand*{\normallocation}{normal location}
\newcommand*{\makefancyindex}[3]{%
  \ifx\normallocation#2%
    \index[#1]{#3}%
  \else
    \index[#1]{???: #3}%
  \fi
}

\newcommand*{\genidx}[2][\normallocation]{\makefancyindex{general}{#1}{#2}}

\newcommand*{\seexref}[2]{\textit{see\/} #1}
\newcommand*{\makefancyreference}[4]{\index[#1]{#3|#2{#4}}}

\newcommand*{\gensee}[2]{\makefancyreference{general}{seexref}{#1}{#2}}

\begin{document}

\chapter[\acronym{GNU} \acronym{FDL}\commonpart]%
{\label{sec:fdl}%
  \genidx{GNU Free Documentation License@\acronym{GNU} Free Documentation License}%
  \gensee{GNU FDL@\acronym{GNU} \acronym{FDL}}{\acronym{GNU} Free Documentation License}%
  \gensee{FDL@\acronym{FDL}}{\acronym{GNU} Free Documentation License}%
  The \acronym{GNU} Free Documentation License\commonpart}

\end{document}