CLion setting CMAKE_CXX_COMPILER in ToolChain.cmake destroy other variables without warning or error

I have make a complete minimum test case available as a tar file but have not found how to upload it,

so here is my ToolChain

# to use this toolchain file 
# cmake -DCMAKE_TOOLCHAIN_FILE=ToolChain.cmake etc..

set(CMAKE_CXX_STANDARD 11)

# following line if activated , make disappears the ITK_DIR Variable
#set(CMAKE_CXX_COMPILER /opt/intel/bin/icpc)

my cmake option in settings

-DITK_DIR=/home/test/itkbuild -DCMAKE_TOOLCHAIN_FILE=/home/bgy/work2017/testcaseClion/ToolChain.cmake

ITK_DIR is set or not depending on the settings of

# following line if activated , make disappears the ITK_DIR Variable
#set(CMAKE_CXX_COMPILER /opt/intel/bin/icpc)