CppTools: Fix thread-unsafe call to MessageManager::write()

The Preprocessor running in a worker thread can call this function.

Fixes: QTCREATORBUG-21481
Change-Id: I4970379fbabae23cfa3d7c1222e81a4ae8c3e6ad
Reviewed-by: Eike Ziller <eike.ziller@qt.io>
Reviewed-by: Marco Bubke <marco.bubke@qt.io>

src/plugins/cpptools/cpptoolsreuse.cpp

@@ -258,7 +258,20 @@ bool fileSizeExceedsLimit(const QFileInfo &fileInfo, int sizeLimitInMb)
                     "CppIndexer",
                     "C++ Indexer: Skipping file \"%1\" because it is too big.")
                         .arg(absoluteFilePath);
-        Core::MessageManager::write(msg, Core::MessageManager::Silent);
+
+#if (QT_VERSION >= QT_VERSION_CHECK(5, 10, 0))
+        QMetaObject::invokeMethod(Core::MessageManager::instance(), [msg]() {
+            Core::MessageManager::write(msg, Core::MessageManager::Silent);
+        });
+#else
+        QMetaObject::invokeMethod(Core::MessageManager::instance(),
+                                  "write",
+                                  Qt::QueuedConnection,
+                                  Q_ARG(QString, msg),
+                                  Q_ARG(Core::MessageManager::PrintToOutputPaneFlags,
+                                        Core::MessageManager::Silent));
+#endif
+
         qWarning().noquote() << msg;
         return true;
     }