Replace signals with Q_SIGNALS

src/engine/enginebase.h

@@ -162,7 +162,7 @@ class EngineBase : public QObject {
   virtual void SetEqualizerEnabled(const bool) {}
   virtual void SetEqualizerParameters(const int, const QList<int>&) {}
 
- signals:
+ Q_SIGNALS:
   // Emitted when crossfading is enabled and the track is crossfade_duration_ away from finishing
   void TrackAboutToEnd();
 

src/engine/gstenginepipeline.h

@@ -141,7 +141,7 @@ class GstEnginePipeline : public QObject {
  public slots:
   void SetFaderVolume(const qreal volume);
 
- signals:
+ Q_SIGNALS:
   void Error(const int pipeline_id, const int domain, const int error_code, const QString &message, const QString &debug);
 
   void EndOfStreamReached(const int pipeline_id, const bool has_next_track);