Detect V4L availability

Do not build related stuff if not found.
Makes GStreamer support available on Hurd.

Task-number: QTBUG-39762
Change-Id: I1f70b6975e5bef99ab2441aac4d90508bc8b64bd
Reviewed-by: Lisandro Damián Nicanor Pérez Meyer <perezmeyer@gmail.com>
Reviewed-by: Yoann Lopes <yoann.lopes@digia.com>

src/plugins/gstreamer/camerabin/camerabin.pro

@@ -81,6 +81,8 @@ config_gstreamer_photography {
     DEFINES += GST_USE_UNSTABLE_API #prevents warnings because of unstable photography API
 }
 
+config_linux_v4l: DEFINES += USE_V4L
+
 OTHER_FILES += \
     camerabin.json
 

src/plugins/gstreamer/camerabin/camerabinserviceplugin.cpp

@@ -51,7 +51,10 @@
 #include <private/qgstutils_p.h>
 
 #include <private/qcore_unix_p.h>
+
+#if defined(USE_V4L)
 #include <linux/videodev2.h>
+#endif
 
 QT_BEGIN_NAMESPACE
 
@@ -132,6 +135,7 @@ void CameraBinServicePlugin::updateDevices() const
     m_cameraDevices.clear();
     m_cameraDescriptions.clear();
 
+#if defined(USE_V4L)
     QDir devDir("/dev");
     devDir.setFilter(QDir::System);
 
@@ -173,6 +177,7 @@ void CameraBinServicePlugin::updateDevices() const
 
     if (!m_cameraDevices.isEmpty())
         m_defaultCameraDevice = m_cameraDevices.first();
+#endif
 }
 
 QT_END_NAMESPACE