$ export PATH=$PATH:/opt/toolchains/gcc-linaro-aarch64-none-elf-4.9-2014.09_linux/bin
$ export PATH=$PATH:/opt/toolchains/gcc-linaro-arm-none-eabi-4.8-2014.04_linux/bin
$ export PATH=$PATH:/opt/toolchains/gcc-linaro-6.3.1-2017.05-x86_64_aarch64-linux-gnu/bin