How to configure ev3dev CMake to use cross compiler - cmake

Question

I am attempting to build the ev3dev C++ bindings (see https://github.com/ddemidov/ev3dev-lang-cpp) for my EV3. But CMake isn't using my cross-compiler toolchain. I've successfully installed the code sourcery toolchain, built a simple hello world app, and run it on my brick. That works just fine. The trouble is that CMake uses my host's g++ compiler instead of the toolchain. I'm familiar with linux and cross-compilers, but I'm a total CMake noob. So I suspect CMake is where I'm going wrong.
I've added the following lines into CMakeLists.txt:
set(CMAKE_C_COMPILER "/cygdrive/c/Users/me/MentorGraphics/Sourcery_CodeBench_Lite_for_ARM_GNU_Linux/bin/arm-none-linux-gnueabi-gcc.exe")
set(CMAKE_CXX_COMPILER "/cygdrive/c/Users/me/MentorGraphics/Sourcery_CodeBench_Lite_for_ARM_GNU_Linux/bin/arm-none-linux-gnueabi-g++.exe")
Here's the host gcc compiler:
$ gcc --version
gcc (GCC) 5.4.0
Copyright (C) 2015 Free Software Foundation, Inc.
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
And the target toolchain gcc compiler:
$ /cygdrive/c/Users/me/MentorGraphics/Sourcery_CodeBench_Lite_for_ARM_GNU_Linux/bin/arm-none-linux-gnueabi-gcc.exe --version
arm-none-linux-gnueabi-gcc.exe (Sourcery CodeBench Lite 2014.05-29) 4.8.3 20140320 (prerelease)
Copyright (C) 2013 Free Software Foundation, Inc.
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
The compilers are different versions, so they are really easy to distinguish.
Now here's the terminal session for the cmake build:
$ mkdir build
$ cd build
$ cmake ../ -DEV3DEV_PLATFORM=EV3
-- No build type selected, default to RelWithDebInfo
-- The C compiler identification is GNU 5.4.0
-- The CXX compiler identification is GNU 5.4.0
CMake Warning at /usr/share/cmake-3.6.2/Modules/Platform/CYGWIN.cmake:15 (message):
CMake no longer defines WIN32 on Cygwin!
(1) If you are just trying to build this project, ignore this warning or
quiet it by setting CMAKE_LEGACY_CYGWIN_WIN32=0 in your environment or in
the CMake cache. If later configuration or build errors occur then this
project may have been written under the assumption that Cygwin is WIN32.
In that case, set CMAKE_LEGACY_CYGWIN_WIN32=1 instead.
(2) If you are developing this project, add the line
set(CMAKE_LEGACY_CYGWIN_WIN32 0) # Remove when CMake >= 2.8.4 is required
at the top of your top-level CMakeLists.txt file or set the minimum
required version of CMake to 2.8.4 or higher. Then teach your project to
build on Cygwin without WIN32.
Call Stack (most recent call first):
/usr/share/cmake-3.6.2/Modules/CMakeSystemSpecificInformation.cmake:36 (include)
CMakeLists.txt:7 (project)
-- Check for working C compiler: /usr/bin/cc
-- Check for working C compiler: /usr/bin/cc -- works
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Detecting C compile features
-- Detecting C compile features - done
-- Check for working CXX compiler: /usr/bin/c++.exe
-- Check for working CXX compiler: /usr/bin/c++.exe -- works
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- Configuring done
-- Generating done
-- Build files have been written to: /cygdrive/c/Users/me/Documents/AppProjects/ev3dev-lang-cpp/build
$
CMake is clearly using the cygwin host gcc/g++ compiler even though I've attempted to configure it to use the toolchain. Where am I going wrong?
EDIT: This is not a duplicate of cmake: problems specifying the compiler (2). I did actually use google, and the cross-compiling instructions on the CMake wiki (https://cmake.org/Wiki/CMake_Cross_Compiling) explicitly dictate using SET(). The problem turned out to be that CMake requires the compiler to be set before PROJECT(). I just moved the SET() lines up above PROJECT() and then CMake found the compiler.