Make it clear which functions that are intended to be translation unit local

Do not share functions that are meant to be translation unit local with
other translation units. Use internal linkage for those consistently.

src/test/bip32_tests.cpp

@@ -87,7 +87,7 @@ TestVector test3 =
      "xprv9uPDJpEQgRQfDcW7BkF7eTya6RPxXeJCqCJGHuCJ4GiRVLzkTXBAJMu2qaMWPrS7AANYqdq6vcBcBUdJCVVFceUvJFjaPdGZ2y9WACViL4L",
       0);
 
-void RunTest(const TestVector &test) {
+static void RunTest(const TestVector &test) {
     std::vector<unsigned char> seed = ParseHex(test.strHexMaster);
     CExtKey key;
     CExtPubKey pubkey;