C++: Fix resolving ui_* files in CppPreprocessor

The working copy contains the artificial ui_* files and therefore we
have to consider it while resolving include files.

Task-number: QTCREATORBUG-9683
Change-Id: Icb3387b4cd885b3652bae3f1da465d3e0f633332
Reviewed-by: Christian Stenger <christian.stenger@digia.com>
Reviewed-by: Eike Ziller <eike.ziller@digia.com>
Reviewed-by: Daniel Teske <daniel.teske@digia.com>
Reviewed-by: Robert Loehning <robert.loehning@digia.com>
Reviewed-by: Erik Verbruggen <erik.verbruggen@digia.com>

src/plugins/cpptools/cpppreprocessor.cpp

@@ -231,7 +231,7 @@ QString CppPreprocessor::resolveFile_helper(const QString &fileName, IncludeType
 
     foreach (const QString &includePath, m_includePaths) {
         QString path = includePath + fileName;
-        if (checkFile(path))
+        if (m_workingCopy.contains(path) || checkFile(path))
             return path;
     }