QPromise/QFutureInterface: in Qt 7 take std::exception_ptr by const-ref

std::exception_ptr is a reference-counted "smart pointer", so we
shouldn't copy it around freely. Unfortunately QFutureInterface
has exported functions taking it by value, so we can't just change
the signatures and keep BC. Simply prepare the code for Qt 7.

Change-Id: Ic5aae6a095c8c842872a40db440c99d2dfe371f1
Reviewed-by: Sona Kurazyan <sona.kurazyan@qt.io>
Reviewed-by: Andrei Golubev <andrei.golubev@qt.io>

src/corelib/thread/qfutureinterface.cpp

@@ -351,7 +351,11 @@ void QFutureInterfaceBase::reportException(const QException &exception)
     }
 }
 
+#if QT_VERSION < QT_VERSION_CHECK(7, 0, 0)
 void QFutureInterfaceBase::reportException(std::exception_ptr exception)
+#else
+void QFutureInterfaceBase::reportException(const std::exception_ptr &exception)
+#endif
 {
     QMutexLocker locker(&d->m_mutex);
     if (d->state.loadRelaxed() & (Canceled|Finished))

src/corelib/thread/qfutureinterface.h

@@ -107,7 +107,11 @@ public:
     void reportCanceled();
 #ifndef QT_NO_EXCEPTIONS
     void reportException(const QException &e);
+#if QT_VERSION < QT_VERSION_CHECK(7, 0, 0)
     void reportException(std::exception_ptr e);
+#else
+    void reportException(const std::exception_ptr &e);
+#endif
 #endif
     void reportResultsReady(int beginIndex, int endIndex);
 

src/corelib/thread/qpromise.h

@@ -85,7 +85,11 @@ public:
     }
 #ifndef QT_NO_EXCEPTIONS
     void setException(const QException &e) { d.reportException(e); }
+#if QT_VERSION < QT_VERSION_CHECK(7, 0, 0)
     void setException(std::exception_ptr e) { d.reportException(e); }
+#else
+    void setException(const std::exception_ptr &e) { d.reportException(e); }
+#endif
 #endif
     void start() { d.reportStarted(); }
     void finish() { d.reportFinished(); }

src/corelib/thread/qpromise.qdoc

@@ -142,10 +142,17 @@
     \sa isCanceled()
 */
 
+#if QT_VERSION < QT_VERSION_CHECK(7, 0, 0)
 /*! \fn template<typename T> void QPromise<T>::setException(std::exception_ptr e)
 
     \overload
 */
+#else
+/*! \fn template<typename T> void QPromise<T>::setException(const std::exception_ptr &e)
+
+    \overload
+*/
+#endif
 
 /*! \fn template<typename T> void QPromise<T>::start()