mpack: fix up broken paths

pkgs/tools/networking/mpack/default.nix

@@ -1,4 +1,4 @@
-{ stdenv, fetchurl, pkgconfig, glib }:
+{ stdenv, fetchurl }:
 
 stdenv.mkDerivation rec {
   name = "mpack-1.6";
@@ -10,10 +10,31 @@ stdenv.mkDerivation rec {
 
   patches = [ ./build-fix.patch ];
 
-  preConfigure = "configureFlags=--mandir=$out/share/man";
+  postPatch = ''
+    for f in *.{c,man,pl,unix} ; do
+      substituteInPlace $f --replace /usr/tmp /tmp
+    done
 
-  meta = {
+    for f in unixpk.c ; do
+      substituteInPlace $f \
+        --replace /usr/sbin /run/current-system/sw/bin
+    done
+
+    # this just shuts up some warnings
+    for f in {decode,encode,part,unixos,unixpk,unixunpk,xmalloc}.c ; do
+      sed -i 'i#include <stdlib.h>' $f
+    done
+  '';
+
+  postInstall = ''
+    install -Dm644 -t $out/share/doc/mpack INSTALL README.*
+  '';
+
+  enableParallelBuilding = true;
+
+  meta = with stdenv.lib; {
     description = "Utilities for encoding and decoding binary files in MIME";
-    platforms = stdenv.lib.platforms.linux;
+    license = licenses.free;
+    platforms = platforms.linux;
   };
 }