adding metadata, putting version in name

pkgs/development/compilers/gcc/gfortran-darwin.nix

@@ -1,15 +1,13 @@
-# This is a derivation customized to work on OS X (Darwin).
+# This is a derivation specific to OS X (Darwin). It may work on other
+# systems as well but has not been tested.
 {gmp, mpfr, libmpc, fetchurl, stdenv}:
 
-# This package is only intended for OSX.
-assert stdenv.isDarwin;
-
 stdenv.mkDerivation rec {
-  name = "gfortran";
+  name = "gfortran-${version}";
   version = "5.1.0";
   buildInputs = [gmp mpfr libmpc];
   src = fetchurl {
-    url = "https://ftp.gnu.org/gnu/gcc/gcc-${version}/gcc-${version}.tar.bz2";
+    url = "mirror://gnu/gcc/gcc-${version}/gcc-${version}.tar.bz2";
     sha256 = "1bd5vj4px3s8nlakbgrh38ynxq4s654m6nxz7lrj03mvkkwgvnmp";
   };
   configureFlags = ''
@@ -19,4 +17,10 @@ stdenv.mkDerivation rec {
     --with-mpc=${libmpc}
   '';
   makeFlags = ["CC=clang"];
+  meta = with stdenv.lib; {
+    description = "GNU Fortran compiler, part of the GNU Compiler Collection.";
+    homepage    = "https://gcc.gnu.org/fortran/";
+    license     = licenses.gpl3Plus;
+    platforms   = platforms.darwin;
+  };
 }