Don't access static functions/fields via instance

Courtesy of readability-static-accessed-through-instance

Change-Id: I71f54244f1e091315dac2943d9e1bfad6efa56a9
Reviewed-by: Jarek Kobus <jaroslaw.kobus@qt.io>

src/libs/cplusplus/pp-engine.cpp

@@ -2029,7 +2029,7 @@ void Preprocessor::handleIfDefDirective(bool checkUndefined, PPToken *tk)
                     value = false; // take the branch
                 }
             }
-        } else if (m_env->isBuiltinMacro(macroName)) {
+        } else if (Environment::isBuiltinMacro(macroName)) {
             value = true;
         }