Run catkin make with custom compiler

edit

I found the most easy way to change the compiler CMake uses, is by adding the following to the respective CMakeList.txt file:

set(CMAKE_CXX_COMPILER "clang++")
set(CMAKE_C_COMPILER "clang")

Have you tried using a toolchain.cmake file?

Here is an example (for cross-compiling to the raspberry pi), I set the arm cross compiler:

set(CMAKE_SYSTEM_NAME Linux)
set(CMAKE_C_COMPILER arm-linux-gnueabi-gcc)
set(CMAKE_CXX_COMPILER arm-linux-gnueabi-g++-4.4)
set(CMAKE_FIND_ROOT_PATH $ENV{HOME}/rpi/tools/arm-bcm2708/arm-bcm2708-linux-gnueabi/arm-bcm2708-linux-gnueabi/sysroot $ENV{HOME}/rpi/rootfs $ENV{HOME}/rpi/rootfs/e2fsprogs-1.42.9 $ENV{HOME}/rpi/rootfs/usr $ENV{HOME}/rpi/rootfs/usr/lib $ENV{HOME}/rpi/rootfs/usr/include $ENV{HOME}/rpi/ros_catkin_ws/install_isolated)
#SET( CMAKE_CXX_FLAGS  "${CMAKE_CXX_FLAGS} -mfpu=vfp -mfloat-abi=softfp -mcpu=arm1176jzf-s" )
#SET( CMAKE_EXE_LINKER_FLAGS  "${CMAKE_EXE_LINKER_FLAGS} -static" )
# Have to set this one to BOTH, to allow CMake to find python
set(CMAKE_FIND_ROOT_PATH_MODE_PROGRAM BOTH)
set(CMAKE_FIND_ROOT_PATH_MODE_LIBRARY ONLY)
set(CMAKE_FIND_ROOT_PATH_MODE_INCLUDE ONLY)

Then, I invoke it with:

catkin_make_isolated --cmake-args -DCMAKE_TOOLCHAIN_FILE=/home/myuser/rpi/toolchain.raspi.cmake

I'm trying to do it in a similar way to Stefanct, but it doesn't work for me. So far, only the command line option works, as per how William described it.
By the time catkin_make gets to the set command in my CMakeList.txt file, its already chosen to use /usr/bin/cc and /usr/bin/c++ and gives an error c++: error: unrecognized command line option ‘-stdlib=libc++’ when I try to perform set(CMAKE_CXX_FLAGS "-v -std=c++11 -stdlib=libc++").
I set the flag in a slightly different way; by checking if clang is available before setting it.

find_program(CLANGPP clang++ HINTS /usr/local/bin /usr/bin /opt/local/bin)
if(${CLANGPP} MATCHES "clang")
set(CXX ${CLANGPP})
set(MAKE_CXX_COMPILER ${CLANGPP})
message(STATUS "CXX = ${CXX}")
endif(${CLANGPP} MATCHES "clang")

and the same for 'clang'.

I'm still trying different things, and when I get it working, I'll come back.

@stefanct, where in your CMakeList.txt file do you put those lines? Do you have an initialisation function?