Don't put QString in static attributes

It crashed in some places on our code-base due to the so-called "static
initialization order fiasco".
As a solution, it turns the variable into a function. This shouldn't have
a penalty due to QStringLiteral.

Change-Id: I9f8a955afdff878dc2f0db16fec861d81250c243
Reviewed-by: Tobias Hunger <tobias.hunger@theqtcompany.com>

src/libs/cplusplus/pp-engine.cpp

@@ -734,7 +734,7 @@ void Preprocessor::State::updateIncludeGuardState_helper(IncludeGuardStateHint h
 #endif // DEBUG_INCLUDE_GUARD_TRACKING
 }
 
-const QString Preprocessor::configurationFileName = QLatin1String("<configuration>");
+QString Preprocessor::configurationFileName() { return QStringLiteral("<configuration>"); }
 
 Preprocessor::Preprocessor(Client *client, Environment *env)
     : m_client(client)
@@ -1978,7 +1978,7 @@ void Preprocessor::handleIfDefDirective(bool checkUndefined, PPToken *tk)
 
             // the macro is a feature constraint(e.g. QT_NO_XXX)
             if (checkUndefined && macroName.startsWith("QT_NO_")) {
-                if (macro->fileName() == configurationFileName) {
+                if (macro->fileName() == configurationFileName()) {
                     // and it' defined in a pro file (e.g. DEFINES += QT_NO_QOBJECT)
 
                     value = false; // take the branch