Fix gcc warnings

plugins/channelrx/demodadsb/adsbdemodgui.cpp

@@ -408,7 +408,6 @@ QString Aircraft::getLabel(const ADSBDemodSettings *settings) const
         if (m_altitudeValid)
         {
             QStringList row1;
-            int transitionAlt = 6500;
             QChar c = m_altitude >= settings->m_transitionAlt ? 'F' : 'A';
             // Convert altitude to flight level
             int fl = m_altitude / 100;

plugins/channelrx/demodam/amdemodgui.cpp

@@ -286,7 +286,6 @@ void AMDemodGUI::on_deltaFrequency_changed(qint64 value)
     (void) value;
 
     qint64 offset = 0;
-    bool valid = true;
 
     if (m_settings.m_frequencyMode == AMDemodSettings::Offset)
     {

plugins/channelrx/freqscanner/freqscanneraddrangedialog.cpp

@@ -27,6 +27,8 @@ FreqScannerAddRangeDialog::FreqScannerAddRangeDialog(int step, QWidget* parent)
     QDialog(parent),
     ui(new Ui::FreqScannerAddRangeDialog)
 {
+    (void) step;
+
     ui->setupUi(this);
 
     ui->start->setColorMapper(ColorMapper(ColorMapper::GrayGold));

plugins/feature/startracker/startrackergui.cpp

@@ -1942,7 +1942,7 @@ void StarTrackerGUI::plotElevationPolarChart()
         // Plot rotator position
         QString ourSourceName = QString("F0:%1 %2").arg(m_starTracker->getIndexInFeatureSet()).arg(m_starTracker->getIdentifier());  // Only one feature set in practice?
         std::vector<FeatureSet*>& featureSets = MainCore::instance()->getFeatureeSets();
-        for (int featureSetIndex = 0; featureSetIndex < featureSets.size(); featureSetIndex++)
+        for (int featureSetIndex = 0; featureSetIndex < (int)featureSets.size(); featureSetIndex++)
         {
             FeatureSet *featureSet = featureSets[featureSetIndex];
             for (int featureIndex = 0; featureIndex < featureSet->getNumberOfFeatures(); featureIndex++)