fpc: switch sf downloads to mirror://

This allows fallback to all configured mirrors for sourceforge
to download, instead of relying on just downloads.sourceforge.net

pkgs/development/compilers/fpc/binary.nix

@@ -6,12 +6,12 @@ stdenv.mkDerivation {
   src =
     if stdenv.system == "i686-linux" then
       fetchurl {
-        url = "http://sourceforge.net/projects/freepascal/files/Linux/2.6.0/fpc-2.6.0.i386-linux.tar";
+        url = "mirror://sourceforge/project/freepascal/Linux/2.6.0/fpc-2.6.0.i386-linux.tar";
         sha256 = "08yklvrfxvk59bxsd4rh1i6s3cjn0q06dzjs94h9fbq3n1qd5zdf";
       }
     else if stdenv.system == "x86_64-linux" then
       fetchurl {
-        url = "http://sourceforge.net/projects/freepascal/files/Linux/2.6.0/fpc-2.6.0.x86_64-linux.tar";
+        url = "mirror://sourceforge/project/freepascal/Linux/2.6.0/fpc-2.6.0.x86_64-linux.tar";
         sha256 = "0k9vi75k39y735fng4jc2vppdywp82j4qhzn7x4r6qjkad64d8lx";
       }
     else throw "Not supported on ${stdenv.system}.";