lilypond: add a workaround for fontforge version detection

A part of Fontforge store path was taken as a part of the version by
configure script leading to a version check failure.

pkgs/misc/lilypond/default.nix

@@ -25,6 +25,11 @@ stdenv.mkDerivation rec{
 
   preConfigure=''
     sed -e "s@mem=mf2pt1@mem=$PWD/mf/mf2pt1@" -i scripts/build/mf2pt1.pl
+
+    # At some point our fontforge had path 2n…-fontforge-2015… and it
+    # confused the version detection…
+    sed -re 's%("[$]exe" --version .*)([|\\] *$)%\1 | sed -re "s@/nix/store/[a-z0-9]{32}-@@" \2%' \
+      -i configure
   '';
 
   postInstall = ''