buildroot

lirc-tools: fix build issue related to clock_gettime()

In some older versions of glibc, clock_gettime() is in librt, so we need
to link with librt when clock_gettime() is used. This commit adds a
lirc-tools patch to make sure we link with librt when needed.

Fixes:

  http://autobuild.buildroot.net/results/2770360880c9b265c8e019141925e56c35ba22dc/

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