/usr/lib/clang/6.0/include is in libclang-common-6.0-dev 1:6.0-1ubuntu2.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/clang/6.0/../../llvm-6.0/lib/clang/6.0.0/include
/usr/lib/clang/6.0/../../llvm-6.0/lib/clang/6.0.0/include