build opencv failed for arm64 architecture

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I am now building opencv 2.4.8 library for iPhone with xcode 5. When I build the architecture "armv7","armv7s" and "i386" with cmake toolchain, everything is fine. But when I want to build for the architecture of "arm64", I have:

 C++ Compiler:                CMAKE_CXX_COMPILER-NOTFOUND  (ver 5.1.0)

It seems that it cannot find the c++compiler. More detailed error messages are as follows:

-- Setting up iPhoneOS toolchain
-- iPhoneOS toolchain loaded
-- The CXX compiler identification is Clang 5.1.0
-- The C compiler identification is Clang 5.1.0 
CMAKE_LIBRARY_PATH=/lib;/usr/lib
-- Looking for linux/videodev.h
CMake Error at /Applications/CMake 2.8-11.app/Contents/share/cmake-2.8/Modules/CMakeCInformation.cmake:37 (get_filename_component):
  get_filename_component called with incorrect number of arguments
Call Stack (most recent call first):
  CMakeLists.txt:3 (PROJECT)


CMake Error: Internal CMake error, TryCompile configure of cmake failed

-- Looking for linux/videodev.h - not found
-- Looking for linux/videodev2.h
CMake Error at /Applications/CMake 2.8-11.app/Contents/share/cmake-2.8/Modules/CMakeCInformation.cmake:37 (get_filename_component):
  get_filename_component called with incorrect number of arguments
Call Stack (most recent call first):
  CMakeLists.txt:3 (PROJECT)


CMake Error: Internal CMake error, TryCompile configure of cmake failed

Any ideas? Thanks.