Eliminate QSystemLocaleSingleton and QSystemLocale(bool)

They are no longer needed. The global static will only ever be
instantiated if and when the QSystemLocale stack is empty; it will
then survive to the end of run-time, serving as a bottom-of-stack
instance that will always be fallen back to after any other instances'
lifetimes. It can thus be a local static of the only function that
accesses it.

Change-Id: I21a1623728b25b46da6e25db9bb973c507a39ca3
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>

src/corelib/text/qlocale.cpp

@@ -60,13 +60,6 @@ using namespace Qt::StringLiterals;
 
 #ifndef QT_NO_SYSTEMLOCALE
 Q_CONSTINIT static QSystemLocale *_systemLocale = nullptr;
-class QSystemLocaleSingleton: public QSystemLocale
-{
-public:
-    QSystemLocaleSingleton() : QSystemLocale(true) {}
-};
-
-Q_GLOBAL_STATIC(QSystemLocaleSingleton, QSystemLocale_globalSystemLocale)
 Q_CONSTINIT static QLocaleData systemLocaleData = {};
 #endif
 
@@ -721,12 +714,6 @@ QSystemLocale::QSystemLocale() : next(_systemLocale)
     systemLocaleData.m_language_id = 0;
 }
 
-/*!
-    \internal
-*/
-QSystemLocale::QSystemLocale(bool)
-{ }
-
 /*!
     \internal
     Deletes the object.
@@ -750,7 +737,12 @@ static const QSystemLocale *systemLocale()
 {
     if (_systemLocale)
         return _systemLocale;
-    return QSystemLocale_globalSystemLocale();
+
+    // As this is only ever instantiated with _systemLocale null, it is
+    // necessarily the ->next-most in any chain that may subsequently develop;
+    // and it won't be destructed until exit()-time.
+    static QSystemLocale globalInstance;
+    return &globalInstance;
 }
 
 static void updateSystemPrivate()

src/corelib/text/qlocale_p.h

@@ -103,9 +103,6 @@ public:
 
     virtual QLocale fallbackLocale() const;
     inline qsizetype fallbackLocaleIndex() const;
-private:
-    QSystemLocale(bool);
-    friend class QSystemLocaleSingleton;
 };
 Q_DECLARE_TYPEINFO(QSystemLocale::QueryType, Q_PRIMITIVE_TYPE);
 Q_DECLARE_TYPEINFO(QSystemLocale::CurrencyToStringArgument, Q_RELOCATABLE_TYPE);