libiio: Add a patch to fix compilation with old glibc

Cherry-picked from upstream.

Fixes:

  http://autobuild.buildroot.net/results/fa7f7db861c342f4d189f74b983ae9d2751cf29b/

Signed-off-by: Paul Cercueil <paul.cercueil@analog.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/libiio/0002-CMake-Link-with-librt-if-found.patch

@@ -0,0 +1,30 @@
+From 1bc450179a0819970261e6a29071756d09b71c5f Mon Sep 17 00:00:00 2001
+From: Paul Cercueil <paul.cercueil@analog.com>
+Date: Fri, 19 Aug 2016 09:00:58 +0200
+Subject: [PATCH] CMake: Link with librt if found
+
+This is required for older versions of glibc.
+
+Signed-off-by: Paul Cercueil <paul.cercueil@analog.com>
+---
+ CMakeLists.txt | 4 ++++
+ 1 file changed, 4 insertions(+)
+
+diff --git a/CMakeLists.txt b/CMakeLists.txt
+index 2a339fe..3dd3520 100644
+--- a/CMakeLists.txt
++++ b/CMakeLists.txt
+@@ -113,6 +113,10 @@ add_definitions(-DLIBIIO_VERSION_GIT="${LIBIIO_VERSION_GIT}")
+ if(WITH_LOCAL_BACKEND)
+ 	add_definitions(-DLOCAL_BACKEND=1)
+ 	set(LIBIIO_CFILES ${LIBIIO_CFILES} local.c)
++
++	# Link with librt if present
++	find_library(LIBRT_LIBRARIES rt)
++	set(LIBS_TO_LINK ${LIBS_TO_LINK} ${LIBRT_LIBRARIES})
+ endif()
+ 
+ find_library(LIBUSB_LIBRARIES usb-1.0)
+-- 
+2.8.1
+