Switch from std::random_shuffle to std::shuffle

std::random_shuffle is removed in C++17; it is replaced by std::shuffle,
which was introduced in C++11. The new ZcashRandomEngine class provides
the Uniform Random Number Generator interface, as inferred from
std::random_device.

src/random.h

@@ -9,6 +9,7 @@
 #include "uint256.h"
 
 #include <functional>
+#include <limits>
 #include <stdint.h>
 
 /**
@@ -19,6 +20,34 @@ uint64_t GetRand(uint64_t nMax);
 int GetRandInt(int nMax);
 uint256 GetRandHash();
 
+/**
+ * Implementation of a C++ Uniform Random Number Generator, backed by GetRandBytes.
+ */
+class ZcashRandomEngine
+{
+public:
+    typedef uint64_t result_type;
+
+    explicit ZcashRandomEngine() {}
+
+    static constexpr result_type min() {
+        return std::numeric_limits<result_type>::min();
+    }
+    static constexpr result_type max() {
+        return std::numeric_limits<result_type>::max();
+    }
+
+    result_type operator()() {
+        result_type nRand = 0;
+        GetRandBytes((unsigned char*)&nRand, sizeof(nRand));
+        return nRand;
+    }
+
+    double entropy() const noexcept {
+        return 0;
+    }
+};
+
 /**
  * Identity function for MappedShuffle, so that elements retain their original order.
  */

src/wallet/wallet.cpp

@@ -17,6 +17,7 @@
 #include "main.h"
 #include "net.h"
 #include "policy/policy.h"
+#include "random.h"
 #include "rpc/protocol.h"
 #include "rpc/server.h"
 #include "script/script.h"
@@ -27,6 +28,7 @@
 #include "crypter.h"
 #include "wallet/asyncrpcoperation_saplingmigration.h"
 
+#include <algorithm>
 #include <assert.h>
 
 #include <boost/algorithm/string/replace.hpp>
@@ -3306,7 +3308,7 @@ bool CWallet::SelectCoinsMinConf(const CAmount& nTargetValue, int nConfMine, int
     vector<pair<CAmount, pair<const CWalletTx*,unsigned int> > > vValue;
     CAmount nTotalLower = 0;
 
-    random_shuffle(vCoins.begin(), vCoins.end(), GetRandInt);
+    std::shuffle(vCoins.begin(), vCoins.end(), ZcashRandomEngine());
 
     BOOST_FOREACH(const COutput &output, vCoins)
     {