编译安装clang（非完整教程、只是个人的一个记录）
Build LLVM and Clang:
cd llvm-project
mkdir build (in-tree build is not supported)
cd build
cmake -DLLVM_ENABLE_PROJECTS=clang -G "Unix Makefiles" ../llvm
make
This builds both LLVM and Clang for debug mode.
Build LLVM and Clang:
cd llvm-project
mkdir build (in-tree build is not supported)
cd build
cmake -DLLVM_ENABLE_PROJECTS=clang -G "Unix Makefiles" ../llvm
make
This builds both LLVM and Clang for debug mode.
