在CMake上交叉编译到OSX时设置SDK

我正在使用CMake从Linux交叉编译到OSX。为此，我使用了一个工具链文件，因此调用如下所示：

cmake -G 'Unix Makefiles' -DCMAKE_TOOLCHAIN_FILE=./cmake/toolchains/c.apple.universal.cmake .

工具链文件如下所示：

SET(CMAKE_SYSTEM_NAME Darwin)
SET(CMAKE_SYSTEM_PROCESSOR universal)

# set compilers...
INCLUDE("${CMAKE_CURRENT_LIST_DIR}/c.apple.common.cmake")

而另一个：

INCLUDE("${CMAKE_CURRENT_LIST_DIR}/../Modules/CMakeMacroSetCCache.cmake")

# specify the cross compiler
SET_CCACHE(CMAKE_C_COMPILER i686-apple-darwin10-gcc)
SET_CCACHE(CMAKE_CXX_COMPILER i686-apple-darwin10-g++)
SET(CMAKE_RANLIB i686-apple-darwin10-ranlib CACHE STRING "" FORCE)
SET(CMAKE_LIPO i686-apple-darwin10-lipo CACHE STRING "" FORCE)

SET(OSX104_SDK "/usr/lib/apple/SDKs/MacOSX10.4.sdk")
SET(OSX105_SDK "/usr/lib/apple/SDKs/MacOSX10.5.sdk")

# set SDK
SET(CMAKE_OSX_DEPLOYMENT_TARGET )
IF(EXISTS ${OSX104_SDK})
    SET(CMAKE_OSX_SYSROOT ${OSX104_SDK})
ELSEIF(EXISTS ${OSX105_SDK})
    SET(CMAKE_OSX_SYSROOT ${OSX105_SDK})
ELSE()
    MESSAGE(FATAL_ERROR "No OSX SDK found!")
ENDIF()
MESSAGE(STATUS "Using OSX SDK at ${CMAKE_OSX_SYSROOT}")

SET(CMAKE_PREFIX_PATH ${CMAKE_OSX_SYSROOT})
SET(CMAKE_FIND_ROOT_PATH ${CMAKE_PREFIX_PATH})
SET(BOOST_ROOT ${CMAKE_PREFIX_PATH})

# search for programs in the build host directories
SET(CMAKE_FIND_ROOT_PATH_MODE_PROGRAM NEVER)

# for libraries and headers in the target directories
SET(CMAKE_FIND_ROOT_PATH_MODE_LIBRARY ONLY)
SET(CMAKE_FIND_ROOT_PATH_MODE_INCLUDE ONLY)

到目前为止，该方法仍然有效，但是CMake在某种程度上会重置CMAKE_OSX_SYSROOT。我得到的输出是：

-- Set CMAKE_C_COMPILER to /usr/lib/ccache-lipo/i686-apple-darwin10-gcc
-- Set CMAKE_CXX_COMPILER to /usr/lib/ccache-lipo/i686-apple-darwin10-g++
-- Using OSX SDK at /usr/lib/apple/SDKs/MacOSX10.5.sdk
-- Set CMAKE_C_COMPILER to /usr/lib/ccache-lipo/i686-apple-darwin10-gcc
-- Set CMAKE_CXX_COMPILER to /usr/lib/ccache-lipo/i686-apple-darwin10-g++
-- Using OSX SDK at /usr/lib/apple/SDKs/MacOSX10.5.sdk
-- The C compiler identification is GNU
-- The CXX compiler identification is GNU
-- Checking whether C compiler has -isysroot
-- Checking whether C compiler has -isysroot - yes
-- Checking whether C compiler supports OSX deployment target flag
-- Checking whether C compiler supports OSX deployment target flag - yes
-- Check for working C compiler: /usr/lib/ccache-lipo/i686-apple-darwin10-gcc
-- Check for working C compiler: /usr/lib/ccache-lipo/i686-apple-darwin10-gcc -- works
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Checking whether CXX compiler has -isysroot
-- Checking whether CXX compiler has -isysroot - yes
-- Checking whether CXX compiler supports OSX deployment target flag
-- Checking whether CXX compiler supports OSX deployment target flag - yes
-- Check for working CXX compiler: /usr/lib/ccache-lipo/i686-apple-darwin10-g++
-- Check for working CXX compiler: /usr/lib/ccache-lipo/i686-apple-darwin10-g++ -- works
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Used Toolchain definition file '/srv/jenkins/.../cmake/toolchains/c.apple.universal.cmake'
-- Configuring for cross-compiling to Darwin on universal
-- Using platform config cmake/darwin.cmake
-- Checking /Developer/SDKs/MacOSX.sdk/usr/lib/libSystem.B.dylib for possible architectures

最后三行来自CMakeList.txt。使用了正确的工具链文件（仅是一​​条消息），正确设置了SYSTEM_NAME和SYSTEM_PROCESSOR，但OSX SDK错误。相应的CMake代码来自一个宏，该宏将设置CMAKE_OSX_ARCHITECTURES（如果之前未设置的话）（在这种情况下）。该行是：

MESSAGE(STATUS "Checking ${CMAKE_OSX_SYSROOT}/usr/lib/libSystem.B.dylib for possible architectures")

我在这里错误地使用CMake吗？CMake为什么要重置OSX_SYSROOT？根据http://www.cmake.org/cmake/help/v3.0/variable/CMAKE_OSX_SYSROOT.html的介绍，它也应该影响FIND *命令，但我需要设置CMAKE_FIND_ROOT_PATH才能正常工作。

奇怪的是，它昨天起作用了。清理整个构建目录（我也肯定也是昨天做过的）并重新运行CMake现在将重置CMAKE_OSX_SYSROOT。

如果这样做有所不同：在宏的包含结束执行之前调用PROJECT，这表明错误的sysroot。