Don't show checkLibraryFunction warning for types with unusedvar configuration (#4765)

Author: chrchr-github

lib/checkfunctions.cpp

@@ -637,6 +637,9 @@ void CheckFunctions::checkLibraryMatchFunctions()
         if (mSettings->library.podtype(tok->expressionString()))
             continue;
 
+        if (mSettings->library.getTypeCheck("unusedvar", functionName) != Library::TypeCheck::def)
+            continue;
+
         const Token* start = tok;
         while (Token::Match(start->tokAt(-2), "%name% ::"))
             start = start->tokAt(-2);

test/testfunctions.cpp

@@ -1957,6 +1957,11 @@ class TestFunctions : public TestFixture {
               "}\n");
         ASSERT_EQUALS("", errout.str());
 
+        check("auto f() {\n"
+              "    return std::runtime_error(\"abc\");\n"
+              "}\n");
+        ASSERT_EQUALS("", errout.str());
+
         settings = settings_old;
     }