libiio: add patch to fix build on buildbots

On buildbots, the building directory seems to be not a subdir of
a git repo, so a variable expands into an empty string which in turn
results in a syntax error:

--snip--
  -- Looking for in6addr_any - found
  -- Found Git: /data/bowl-builder/arm_cortex-a5/build/sdk/staging_dir/host/bin/git (found version "2.1.4")
  fatal: Not a git repository (or any parent up to mount point /data)
  Stopping at filesystem boundary (GIT_DISCOVERY_ACROSS_FILESYSTEM not set).
  CMake Error at CMakeLists.txt:114 (if):
    if given arguments:

      "STREQUAL" "/data/bowl-builder/arm_cortex-a5/build/sdk/build_dir/target-arm_cortex-a5_musl_eabi/libiio-0.11"

    Unknown arguments specified

  -- Configuring incomplete, errors occurred!
--snap--

The patch quotes the if arguments and thus fixes the build.

Signed-off-by: Michael Heimpold <mhei@heimpold.de>

libs/libiio/patches/001-quote-strequal.patch

@@ -0,0 +1,11 @@
+--- a/CMakeLists.txt	2017-10-23 22:24:46.000000000 +0200
++++ b/CMakeLists.txt	2017-11-18 20:31:27.943838662 +0100
+@@ -111,7 +111,7 @@
+ 		OUTPUT_STRIP_TRAILING_WHITESPACE
+ 	)
+ 
+-	if (${LIBIIO_GIT_REPO} STREQUAL ${CMAKE_CURRENT_SOURCE_DIR})
++	if ("${LIBIIO_GIT_REPO}" STREQUAL "${CMAKE_CURRENT_SOURCE_DIR}")
+ 		execute_process(
+ 			COMMAND ${GIT_EXECUTABLE} rev-parse --short HEAD
+ 			WORKING_DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR}