build: Fix build warnings

Level 15 Debug self play test result:
118503ms/117685ms = 1.007
Reduce 0.7% performance.

src/hashmap.h

@@ -55,7 +55,10 @@ class HashMap
         hashTable = new HashNode<K, V>[hashSize];
 #endif // ALIGNED_LARGE_PAGES
 
-        memset(hashTable, 0, sizeof(HashNode<K, V>) * hashSize);
+        for (size_t i = 0; i < hashSize; i++) {
+            hashTable[i].~HashNode<K, V>();
+            new (&hashTable[i]) HashNode<K, V>();
+        }
 #else  // DISABLE_HASHBUCKET
        // create the key table as an array of key buckets
         hashTable = new HashBucket<K, V>[hashSize];
@@ -151,7 +154,10 @@ class HashMap
     void clear() const
     {
 #ifdef DISABLE_HASHBUCKET
-        memset(hashTable, 0, sizeof(HashNode<K, V>) * hashSize);
+        for (size_t i = 0; i < hashSize; i++) {
+            hashTable[i].~HashNode<K, V>();
+            new (&hashTable[i]) HashNode<K, V>();
+        }
 #else  // DISABLE_HASHBUCKET
         for (size_t i = 0; i < hashSize; i++) {
             (hashTable[i]).clear();

src/position.cpp

@@ -1,14 +1,15 @@
 // position.cpp
 
-#include <algorithm>
-#include <iomanip>
-#include <sstream>
-#include <string> // std::string, std::stoi
-
+#include "search_engine.h"
 #include "mills.h"
 #include "position.h"
 #include "thread.h"
-#include "search_engine.h"
+
+#include <algorithm>
+#include <cstring>
+#include <iomanip>
+#include <sstream>
+#include <string>
 
 using std::string;
 using std::vector;
@@ -550,7 +551,7 @@ void Position::do_move(Move m)
 
 void Position::undo_move(Sanmill::Stack<Position> &ss)
 {
-    memcpy(this, ss.top(), sizeof(Position));
+    *this = *ss.top();
     ss.pop();
 }
 

src/ui/qt/game_ui.cpp

@@ -311,8 +311,7 @@ void Game::updateTips()
         recordGameOverReason();
 
         scoreStr = "Score " + to_string(score[WHITE]) + " : " +
-                   to_string(score[BLACK]) + ", Draw " +
-                   to_string(score[DRAW]);
+                   to_string(score[BLACK]) + ", Draw " + to_string(score[DRAW]);
 
         switch (p.winner) {
         case WHITE: