libv4l: add patch to link qv4l2 tool with librt

The qv4l2 tool in libv4l uses clock_gettime(), so it should link
against librt to build properly with old versions of glibc. Therefore,
we add a patch to libv4l to fix this issue. Autoreconfiguring libv4l
is now necessary since the patch touches Makefile.am.

Fixes:

  http://autobuild.buildroot.net/results/5dff0ec19205e02f6ee373d34cb79f39ac25b609/



Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>