zinnia: fix compilation on darwin, update sourceRoot logic

pkgs/by-name/zi/zinnia/package.nix

···
   fetchFromGitHub,
 }:
 
-stdenv.mkDerivation {
+stdenv.mkDerivation (finalAttrs: {
   pname = "zinnia";
   version = "2016-08-28";
 
···
     sha256 = "1izjy5qw6swg0rs2ym2i72zndb90mwrfbd1iv8xbpwckbm4899lg";
   };
 
-  setSourceRoot = ''
-    sourceRoot=$(echo */zinnia)
-  '';
+  sourceRoot = "${finalAttrs.src.name}/zinnia";
 
-  meta = with lib; {
+  patches = [
+    # Fixes the following error on darwin:
+    # svm.cpp:50:10: error: no member named 'random_shuffle' in namespace 'std'
+    ./remove-random-shuffle-usage.patch
+  ];
+
+  meta = {
     description = "Online hand recognition system with machine learning";
     homepage = "http://taku910.github.io/zinnia/";
-    license = licenses.bsd2;
-    platforms = platforms.unix;
+    license = lib.licenses.bsd2;
+    platforms = lib.platforms.unix;
     maintainers = [ ];
   };
-}
+})

pkgs/by-name/zi/zinnia/remove-random-shuffle-usage.patch

···
+diff --git a/svm.cpp b/svm.cpp
+index 3b7643e..2a34b42 100644
+--- a/svm.cpp
++++ b/svm.cpp
+@@ -10,6 +10,7 @@
+ #include <vector>
+ #include <cmath>
+ #include <algorithm>
++#include <random>
+ #include "feature.h"
+ 
+ namespace zinnia {
+@@ -43,11 +44,13 @@ bool svm_train(size_t l,
+     }
+   }
+ 
++  std::random_device rand_device;
++  std::default_random_engine rand_engine(rand_device());
+   static const size_t kMaxIteration = 2000;
+   for (size_t iter = 0; iter < kMaxIteration; ++iter) {
+     double PGmax_new = -kINF;
+     double PGmin_new = kINF;
+-    std::random_shuffle(index.begin(), index.begin() + active_size);
++    std::shuffle(index.begin(), index.begin() + active_size, rand_engine);
+ 
+     for (size_t s = 0; s < active_size; ++s) {
+       const size_t i = index[s];