rustc --version-详细的rustup目标添加thumbv7em-none-eabihf货物构建--target thumbv7em-none-eabihf rustup覆盖设置每晚rustup组件添加rust-src货物install cargo-xbuild货物xbuild货物安装bootimage --version“ ^ 0.7.7” rustup组件添加llvm-tools-preview货物bootimage qemu-system-x86_64 -drive form