Merge #13294: Fix compiler warnings emitted when compiling under stock OpenBSD 6.3

a426098 Fix compiler warnings emitted when compiling under stock OpenBSD 6.3 (practicalswift)

Pull request description:

  Fix compiler warnings emitted when compiling under stock OpenBSD 6.3 (OpenBSD clang version 5.0.1, based on LLVM 5.0.1):

  ```
  random.cpp:182:13: warning: unused function 'GetDevURandom' [-Wunused-function]
  static void GetDevURandom(unsigned char *ent32)
              ^

  txmempool.cpp:707:45: warning: comparison of integers of different signs: 'uint64_t' (aka 'unsigned long long') and 'long long' [-Wsign-compare]
          assert(it->GetSizeWithDescendants() >= childSizes + it->GetTxSize());
                 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ^  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  ```

Tree-SHA512: da2ae86218054b10659ea694179433700ac91de8022e06007348168ed5adc3d8c4ad3b32a3fc5783a2cdf1ca7425aff586b839200dd3b226ebff72a7df15f120

Author: laanwj

src/txmempool.cpp

@@ -693,18 +693,18 @@ void CTxMemPool::check(const CCoinsViewCache *pcoins) const
         // Check children against mapNextTx
         CTxMemPool::setEntries setChildrenCheck;
         auto iter = mapNextTx.lower_bound(COutPoint(it->GetTx().GetHash(), 0));
-        int64_t childSizes = 0;
+        uint64_t child_sizes = 0;
         for (; iter != mapNextTx.end() && iter->first->hash == it->GetTx().GetHash(); ++iter) {
             txiter childit = mapTx.find(iter->second->GetHash());
             assert(childit != mapTx.end()); // mapNextTx points to in-mempool transactions
             if (setChildrenCheck.insert(childit).second) {
-                childSizes += childit->GetTxSize();
+                child_sizes += childit->GetTxSize();
             }
         }
         assert(setChildrenCheck == GetMemPoolChildren(it));
         // Also check to make sure size is greater than sum with immediate children.
         // just a sanity check, not definitive that this calc is correct...
-        assert(it->GetSizeWithDescendants() >= childSizes + it->GetTxSize());
+        assert(it->GetSizeWithDescendants() >= child_sizes + it->GetTxSize());
 
         if (fDependsWait)
             waitingOnDependants.push_back(&(*it));