Fixed #14129 (false positive: unusedPrivateFunction with __attribute__((unused)))

Author: danmar

lib/checkclass.cpp

@@ -1342,7 +1342,7 @@ void CheckClass::privateFunctions()
 
         while (!privateFuncs.empty()) {
             const auto& pf = privateFuncs.front();
-            if (pf->token->isAttributeMaybeUnused()) {
+            if (pf->token->isAttributeMaybeUnused() || pf->token->isAttributeUnused()) {
                 privateFuncs.pop_front();
                 continue;
             }

test/testunusedprivfunc.cpp

@@ -84,6 +84,7 @@ class TestUnusedPrivateFunction : public TestFixture {
 
         TEST_CASE(templateSimplification); //ticket #6183
         TEST_CASE(maybeUnused);
+        TEST_CASE(attributeUnused); // #14129
         TEST_CASE(trailingReturn);
     }
 
@@ -890,6 +891,13 @@ class TestUnusedPrivateFunction : public TestFixture {
         ASSERT_EQUALS("", errout_str());
     }
 
+    void attributeUnused() {
+        check("class C {\n"
+              "    __attribute__((unused)) int f() { return 42; }\n"
+              "};");
+        ASSERT_EQUALS("", errout_str());
+    }
+
     void trailingReturn() {
         check("struct B { virtual void f(); };\n"
               "struct D : B {\n"