python-3.5: Eliminate -dev paths from the runtime closure

This reduces Python's closure size from 200 MiB to 129 MiB. Even
better would be to get move tkinter to a separate output or package
(since that would get rid of all X11 stuff), but that's a bit harder.

pkgs/development/interpreters/python/cpython/3.5/default.nix

···
     paxmark E $out/bin/python${majorVersion}
   '';
 
+  postFixup = ''
+    # Get rid of retained dependencies on -dev packages, and remove
+    # some $TMPDIR references to improve binary reproducibility.
+    for i in $out/lib//python${majorVersion}/_sysconfigdata.py $out/lib/python${majorVersion}/config-${majorVersion}m/Makefile; do
+      sed -i $i -e "s|-I/nix/store/[^ ']*||g" -e "s|$TMPDIR|/no-such-path|g"
+    done
+
+    # FIXME: should regenerate this.
+    rm $out/lib/python${majorVersion}/__pycache__/_sysconfigdata.cpython*
+  '';
+
   passthru = rec {
     zlibSupport = zlib != null;
     sqliteSupport = sqlite != null;