sentencepiece: split into multiple outputs, optional gperftools

I am using sentencepiece in a downstream application where I want to
minimize the resulting closures. This commit makes changes to make
sentencepiece a leaner dependency:

- Split the outputs, so that the binaries/headers do not end up in the
transitive closure in a library dependency.

- Add the `withGPerfTools` option, which is enabled by default, to
make it possible to disable the gperftools dependency. According to
the sentencepiece README, this dependency gives a 10-40% performance
improvement. But in many cases this is overshadowed by the neural
networks that use piece identifiers as input anyway.

pkgs/development/libraries/sentencepiece/default.nix

···
-{ config
+{ lib
 , fetchFromGitHub
 , stdenv
-, lib
 , cmake
 , gperftools
+
+, withGPerfTools ? true
 }:
 
 stdenv.mkDerivation rec {
···
     sha256 = "1ncvyw9ar0z7nd47cysxg5xrjm01y1shdlhp8l2pdpx059p3yx3w";
   };
 
-  nativeBuildInputs = [ cmake gperftools ];
+  nativeBuildInputs = [ cmake ] ++ lib.optional withGPerfTools gperftools;
+
+  outputs = [ "bin" "dev" "out" ];
 
   meta = with stdenv.lib; {
     homepage = "https://github.com/google/sentencepiece";

pkgs/development/python-modules/sentencepiece/default.nix

···
 
 buildPythonPackage rec {
   pname = "sentencepiece";
-  inherit (sentencepiece) version src meta;
+  inherit (sentencepiece) version src;
 
   nativeBuildInputs = [ pkgconfig ];
-  buildInputs = [ sentencepiece ];
+  buildInputs = [ sentencepiece.dev ];
 
   sourceRoot = "source/python";
+
+  # sentencepiece installs 'bin' output.
+  meta = builtins.removeAttrs sentencepiece.meta [ "outputsToInstall" ];
 }