Fix FP unusedVar with side effects in destructor (#4212)

lib/checkunusedvar.cpp

@@ -1535,7 +1535,7 @@ bool CheckUnusedVar::isRecordTypeWithoutSideEffects(const Type* type)
 
     // Non-empty constructors => possible side effects
     for (const Function& f : type->classScope->functionList) {
-        if (!f.isConstructor())
+        if (!f.isConstructor() && !f.isDestructor())
             continue;
         if (f.argDef && Token::simpleMatch(f.argDef->link(), ") ="))
             continue; // ignore default/deleted constructors

test/testunusedvar.cpp

@@ -536,6 +536,16 @@ private:
             "   F f;\n"
             "}");
         ASSERT_EQUALS("", errout.str());
+
+        functionVariableUsage(
+            "struct S {\n"
+            "    static void f() { std::cout << \"f()\"; }\n"
+            "    ~S() { f(); }\n"
+            "};\n"
+            "void g() {\n"
+            "    S s;\n"
+            "}\n");
+        ASSERT_EQUALS("", errout.str());
     }
 
     void cleanFunction() {