Work around QLocalSocket::error deprecation

Centralizing does not bring much benefit here, it's just six locations,
and having either a central #include <QLocalSocket> in algorithm.h
or a separe file does not sound better.

In any case, it is absurd, that deprecating functions to "make code
nicer" requires spilling #if QT_VERSION_CHECK over the code.

Change-Id: Ia9a8c0eb6ef7cabbaffb46cfe472247e26e7e2c2
Reviewed-by: Eike Ziller <eike.ziller@qt.io>

src/plugins/cmakeprojectmanager/servermode.cpp

@@ -207,8 +207,15 @@ void ServerMode::connectToServer()
 
     auto socket = new QLocalSocket(m_cmakeProcess.get());
     connect(socket, &QLocalSocket::readyRead, this, &ServerMode::handleRawCMakeServerData);
-    connect(socket, QOverload<QLocalSocket::LocalSocketError>::of(&QLocalSocket::error),
-            this, [this, socket]() {
+
+    constexpr void (QLocalSocket::*LocalSocketErrorFunction)(QLocalSocket::LocalSocketError)
+#if QT_VERSION < QT_VERSION_CHECK(5, 15, 0)
+                = &QLocalSocket::error;
+#else
+                = &QLocalSocket::errorOccurred;
+#endif
+
+    connect(socket, LocalSocketErrorFunction, this, [this, socket]() {
         reportError(socket->errorString());
         m_cmakeSocket = nullptr;
         socket->disconnect();