CMake: Use shorter names for local sockets in server-mode

Apparently there is a limit to about 100 characters or so on some
versions of Unix (e.g. Darwin), and there is also the tendency to
point TMPDIR into places very far from '/' (e.g. Darwin), which
can result in the local socket path getting trunkated.

So make sure to put the local socket into /tmp on Unix. That works
on Linux and on Darwin.

Change-Id: I40bfaf932c5013cf72addb5621360e97c9583daa
Reviewed-by: Alexandru Croitor <alexandru.croitor@qt.io>

src/plugins/cmakeprojectmanager/servermode.h

@@ -30,6 +30,7 @@
 #include <QLoggingCategory>
 #include <QTimer>
 #include <QVariantMap>
+#include <QTemporaryDir>
 
 #include <memory>
 
@@ -84,6 +85,9 @@ private:
 
     void reportError(const QString &msg);
 
+#if defined(Q_OS_UNIX)
+    QTemporaryDir m_socketDir;
+#endif
     std::unique_ptr<Utils::QtcProcess> m_cmakeProcess;
     QLocalSocket *m_cmakeSocket = nullptr;
     QTimer m_connectionTimer;
@@ -112,6 +116,7 @@ private:
     const int m_minorProtocol = -1;
 
     int m_requestCounter = 0;
+
 };
 
 } // namespace Internal