set(CLANG_DIR "/opt/llvm/x86_64/3.9.0/bin") set(GCC_TOOLCHAIN_DIR "/opt/gcc/x86_64/6.1.0") set(CMAKE_C_COMPILER "${CLANG_DIR}/clang") set(CMAKE_CXX_COMPILER "${CLANG_DIR}/clang++") set(CMAKE_C_COMPILER_EXTERNAL_TOOLCHAIN ${GCC_TOOLCHAIN_DIR}) set(CMAKE_CXX_COMPILER_EXTERNAL_TOOLCHAIN ${GCC_TOOLCHAIN_DIR})