freecad: fix for devshell

Linking with `gfortrun.cc.lib` instead of `gfortrun.cc`. For unknown
reason previous variant works well withing sandbox. But there was an
issue with building freecad in development shell. The
`${gfortran.cc}/lib` does not contains shared (.so) variants of
libraries but static archives (.a). This leads to invalid linking of
shared library with static archive which was not compiled with `-fPIC`.

Change-Id: I1e0503204ddeb61eb0d5c251beb8ce60d71d20fd

pkgs/by-name/fr/freecad/package.nix

@@ -155,7 +155,7 @@ freecad-utils.makeCustomizable (stdenv.mkDerivation (finalAttrs: {
 
   # This should work on both x86_64, and i686 linux
   preBuild = ''
-    export NIX_LDFLAGS="-L${gfortran.cc}/lib64 -L${gfortran.cc}/lib $NIX_LDFLAGS";
+    export NIX_LDFLAGS="-L${gfortran.cc.lib}/lib64 -L${gfortran.cc.lib}/lib $NIX_LDFLAGS";
   '';
 
   preConfigure = ''