llvm 官方 apt 网站：https://apt.llvm.org/
先执行以下命令：
wget -O - https://apt.llvm.org/llvm-snapshot.gpg.key|sudo apt-key add -
修改 sources.list：
sudo vim /etc/apt/sources.list
1 Focal (20.04) - Last update : Sun, 24 May 2020 18:52:03 UTC / Revision: 20200524052636+1e7865d9464 2 # i386 not available 3 deb http://apt.llvm.org/focal/ llvm-toolchain-focal main 4 deb-src http://apt.llvm.org/focal/ llvm-toolchain-focal main 5 # 9 6 deb http://apt.llvm.org/focal/ llvm-toolchain-focal-9 main 7 deb-src http://apt.llvm.org/focal/ llvm-toolchain-focal-9 main 8 # 10 9 deb http://apt.llvm.org/focal/ llvm-toolchain-focal-10 main 10 deb-src http://apt.llvm.org/focal/ llvm-toolchain-focal-10 main
执行 sudo apt-get update，然后执行安装：
sudo apt-get install clang-format clang-tidy clang-tools clang clangd libc++-dev libc++1 libc++abi-dev libc++abi1 libclang-dev libclang1 liblldb-11-dev libllvm-ocaml-dev libomp-dev libomp5 lld lldb llvm-dev llvm-runtime llvm python-clang