Custom executable RC: Warn about non-existing command.

Show the path in red with corresponding message in tool tip, without
making it a fatal condition.

Task-number: QTCREATORBUG-15998
Change-Id: I5c6ddf3e79ed4b5ff659f0cab0560fcc78f6f6a9
Reviewed-by: Tobias Hunger <tobias.hunger@theqtcompany.com>

src/plugins/qtsupport/customexecutableconfigurationwidget.cpp

@@ -56,7 +56,7 @@ CustomExecutableConfigurationWidget::CustomExecutableConfigurationWidget(CustomE
 
     m_executableChooser = new PathChooser(this);
     m_executableChooser->setHistoryCompleter(QLatin1String("Qt.CustomExecutable.History"));
-    m_executableChooser->setExpectedKind(PathChooser::Command);
+    m_executableChooser->setExpectedKind(PathChooser::ExistingCommand);
     layout->addRow(tr("Executable:"), m_executableChooser);
 
     auto argumentsAspect = rc->extraAspect<ArgumentsAspect>();