/usr/lib/llvm-3.5/include/llvm-c is in llvm-3.5-dev 1:3.5.2-3ubuntu1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/llvm-3.5/include/../../../include/llvm-c-3.5/llvm-c
/usr/lib/llvm-3.5/include/../../../include/llvm-c-3.5/llvm-c