Fix warnings

tests/bases.cpp

@@ -32,8 +32,8 @@ TEST_CASE("Triviality", "[bases.triviality]") {
         struct T {
             T(const T&){}
             T(T&&) {};
-            T& operator=(const T&) {}
-            T& operator=(T&&) {};
+            T& operator=(const T&) { return *this; }
+            T& operator=(T&&) { return *this; };
             ~T(){}
         };
         REQUIRE(!std::is_trivially_copy_constructible<tl::optional<T>>::value);

tests/noexcept.cpp

@@ -80,7 +80,7 @@ TEST_CASE("Noexcept", "[noexcept]") {
     struct throw_move_assign {
       throw_move_assign() = default;
       throw_move_assign(throw_move_assign &&){};
-      throw_move_assign &operator=(const throw_move_assign &) {}
+      throw_move_assign &operator=(const throw_move_assign &) { return *this; }
     };
 
     using nothrow_opt = tl::optional<nothrow_move_assign>;