v4l2: Actually build the plugin

The checks were removed inadvertedly in previous patch and not replaced.
Re-introduce the configure checks and some of the checks in order to enable
this plugin again. We only check if videodev2.h exist on the platform to
avoid building on Windows or OSX, though we build against our own copy. This
was breaking the build on built-bot.

configure.ac

@@ -498,6 +498,21 @@ AG_GST_CHECK_FEATURE(OSX_VIDEO, [OSX video], osxvideosink, [
       ]], [[return 0;]])],[HAVE_OSX_VIDEO="yes"],[HAVE_OSX_VIDEO="no"])
 ])
 
+dnl *** Video 4 Linux 2 ***
+dnl renamed to GST_V4L2 because of some conflict with kernel headers
+translit(dnm, m, l) AM_CONDITIONAL(USE_GST_V4L2, true)
+HAVE_VIDEODEC=no
+AG_GST_CHECK_FEATURE(GST_V4L2, [Video 4 Linux 2], video4linux2, [
+  AC_MSG_CHECKING([Checking for video4linux2 header ...])
+  AC_CHECK_HEADER(linux/videodev2.h, [ HAVE_VIDEODEV=yes ],
+  [
+    AC_CHECK_HEADER(sys/videodev2.h, [ HAVE_VIDEODEV=yes ])
+  ])
+  if test "x$HAVE_VIDEODEV" = "xno"; then
+     AC_MSG_WARN([video4linux2 was not found])
+  fi
+])
+
 # Optional gudev for device probing
 AC_ARG_WITH([gudev],
   AS_HELP_STRING([--with-gudev],[device detection with gudev]),

sys/Makefile.am

@@ -53,6 +53,12 @@ endif
 # QCAM_DIR=
 # endif
 
+if USE_GST_V4L2
+V4L2_DIR=v4l2
+else
+V4L2_DIR=
+endif
+
 # if USE_VCD
 # VCD_DIR=vcd
 # else
@@ -77,7 +83,7 @@ else
 XIMAGE_DIR=
 endif
 
-SUBDIRS=$(DIRECTSOUND_DIR) $(WAVEFORM_DIR) $(OSS_DIR) $(OSS4_DIR) $(OSX_AUDIO_DIR) $(OSX_VIDEO_DIR) $(SUNAUDIO_DIR) $(XIMAGE_DIR)
+SUBDIRS=$(DIRECTSOUND_DIR) $(WAVEFORM_DIR) $(OSS_DIR) $(OSS4_DIR) $(OSX_AUDIO_DIR) $(OSX_VIDEO_DIR) $(SUNAUDIO_DIR) $(V4L_DIR) $(XIMAGE_DIR)
 
 DIST_SUBDIRS=directsound oss oss4 osxaudio osxvideo sunaudio v4l2 waveform ximage