Build Rust environment for ESP32

Recently I heard that LLVM for xtensa is working, so I tried to build Rust for ESP32. (2019-05-16 Translated into English) Source information is, here and here. sudo apt-get install ninja-build export MY_BUILD_ROOT="$HOME/.xtensa" mkdir -p "$MY_BUILD_ROOT" cd "$MY_BUILD_ROOT" git clone https://github.com/espressif/llvm-xtensa.git git clone https://github.com/espressif/clang-xtensa.git llvm-xtensa/