[pkgs] Fixed STREAM build.

pkgs/applications/stream/default.nix

-{ stdenv, src, fetchgit, gfortran }:
+{ stdenv, src, fetchgit, gfortran, pkgconfig }:
 stdenv.mkDerivation {
   inherit src;
   name = "stream";
 
-  nativeBuildInputs = [ gfortran ];
+  nativeBuildInputs = [ gfortran pkgconfig ];
   buildInputs = [ ];
 
+  buildFlags = ''CC=gcc FC=gfortran'';
+
   installPhase = ''
     mkdir -p $out/bin/
     cp stream_c.exe $out/bin