find_boost fails with error in iOS cross-compilation scenario

Hi,

Using the current cmake 3.9.1 searching for boost in a iOS scenario breaks the makefile generation.

Running cmake -Wno-dev -DCMAKE_TOOLCHAIN_FILE=../bin/osx/iOS.cmake -DIOS_PLATFORM=OS -G Xcode .. with the CMakeLists.txt

PROJECT(Pipeline)
cmake_minimum_required(VERSION 3.5)
set(BOOST_ROOT ${CMAKE_SOURCE_DIR}/../boost CACHE PATH "Boost root directory")
set(Boost_VERSION 106400)
find_package(Boost 1.64.0 COMPONENTS thread)

fails with

-- Could NOT find Threads (missing: Threads_FOUND) 
CMake Error in /usr/local/Cellar/cmake/3.9.1/share/cmake/Modules/FindBoost.cmake:
  cmake_policy PUSH without matching POP
Call Stack (most recent call first):
  CMakeLists.txt:6 (find_package)
-- Configuring incomplete, errors occurred!

A cmake trace is attached.

The (complete) CMakeLists.txt that causes the problems used to work with earlier versions of cmake.

Franktrace.txt