CMake: Use new MessageManager API

Flash when CMake is started, write all other output silently.
This avoids re-popping up the general messages pane all the time.

When an error occurs, that is put into the issues pane, so no need
to pop up the general messages pane for that either.

Task-number: QTCREATORBUG-24430
Change-Id: I07ae4182cbc43147fbb343b360baf9da7e65f224
Reviewed-by: Cristian Adam <cristian.adam@qt.io>

src/plugins/cmakeprojectmanager/cmakeprojectmanager.cpp

@@ -281,8 +281,8 @@ void CMakeManager::buildFile(Node *node)
                     bc->buildDirectory());
         targetBase = relativeBuildDir / "CMakeFiles" / (targetNode->displayName() + ".dir");
     } else if (!generator.contains("Makefiles")) {
-        Core::MessageManager::write(tr("Build File is not supported for generator \"%1\"")
-                                    .arg(generator));
+        Core::MessageManager::writeFlashing(
+            tr("Build File is not supported for generator \"%1\"").arg(generator));
         return;
     }