Reduce build warnings and enable Qt build

src/script/script.h

@@ -377,6 +377,7 @@ protected:
 public:
     CScript() { }
     CScript(const CScript& b) : std::vector<unsigned char>(b.begin(), b.end()) { }
+    CScript& operator=(const CScript& b) = default;
     CScript(const_iterator pbegin, const_iterator pend) : std::vector<unsigned char>(pbegin, pend) { }
     CScript(const unsigned char* pbegin, const unsigned char* pend) : std::vector<unsigned char>(pbegin, pend) { }