install clang on Debian 9

install-clang.sh

# Add apt.llvm.org repository and install clang
wget -O - https://apt.llvm.org/llvm-snapshot.gpg.key|sudo apt-key add -
sudo apt-add-repository "deb http://apt.llvm.org/stretch/ llvm-toolchain-stretch main"
sudo apt-get update
sudo apt-get install -y clang clang-format clang-tidy lldb libc++-8-dev libc++abi-8-dev

# Check version
clang --version
clang++ --version

# Use clang as default compiler
sudo update-alternatives --install /usr/bin/cc cc /usr/bin/clang 90
sudo update-alternatives --install /usr/bin/c++ c++ /usr/bin/clang++ 90
sudo update-alternatives --install /usr/bin/cpp cpp /usr/bin/clang++ 90

# Check default compiler tools
cc --version
c++ --version
cpp --version