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/gsttools/gsttools.pro

@@ -100,6 +100,8 @@ config_gstreamer_appsrc {
     LIBS_PRIVATE += -lgstapp-0.10
 }
 
+config_linux_v4l: DEFINES += USE_V4L
+
 HEADERS += $$PRIVATE_HEADERS
 
 DESTDIR = $$QT.multimedia.libs

src/gsttools/qgstreamervideoinputdevicecontrol.cpp

@@ -45,7 +45,10 @@
 #include <QtCore/QDebug>
 
 #include <private/qcore_unix_p.h>
+
+#if defined(USE_V4L)
 #include <linux/videodev2.h>
+#endif
 
 QGstreamerVideoInputDeviceControl::QGstreamerVideoInputDeviceControl(QObject *parent)
     :QVideoDeviceSelectorControl(parent), m_source(0), m_selectedDevice(0)
@@ -118,6 +121,7 @@ void QGstreamerVideoInputDeviceControl::update()
         return;
     }
 
+#if defined(USE_V4L)
     QDir devDir("/dev");
     devDir.setFilter(QDir::System);
 
@@ -158,4 +162,5 @@ void QGstreamerVideoInputDeviceControl::update()
         }
         qt_safe_close(fd);
     }
+#endif
 }