Add actual header file for utilities in gtest/utils.cpp

It's not best practice to not use headers.

src/Makefile.gtest.include

@@ -7,6 +7,7 @@ noinst_PROGRAMS += zcash-gtest
 zcash_gtest_SOURCES = \
 	gtest/main.cpp \
 	gtest/utils.cpp \
+	gtest/utils.h \
 	gtest/test_checktransaction.cpp \
 	gtest/json_test_vectors.cpp \
 	gtest/json_test_vectors.h \

src/gtest/test_random.cpp

@@ -1,9 +1,7 @@
 #include <gtest/gtest.h>
 
 #include "random.h"
-
-extern int GenZero(int n);
-extern int GenMax(int n);
+#include "gtest/utils.h"
 
 TEST(Random, MappedShuffle) {
     std::vector<int> a {8, 4, 6, 3, 5};

src/gtest/test_transaction.cpp

@@ -1,12 +1,11 @@
 #include <gtest/gtest.h>
 
+#include "gtest/utils.h"
 #include "primitives/transaction.h"
 #include "zcash/Note.hpp"
 #include "zcash/Address.hpp"
 
 extern ZCJoinSplit* params;
-extern int GenZero(int n);
-extern int GenMax(int n);
 
 TEST(Transaction, JSDescriptionRandomized) {
     // construct a merkle tree

src/gtest/utils.cpp

@@ -1,3 +1,5 @@
+#include "gtest/utils.h"
+
 int GenZero(int n)
 {
     return 0;

src/gtest/utils.h

@@ -0,0 +1,7 @@
+#ifndef BITCOIN_GTEST_UTILS_H
+#define BITCOIN_GTEST_UTILS_H
+
+int GenZero(int n);
+int GenMax(int n);
+
+#endif