/usr/include/viennacl/linalg/detail/ is in libviennacl-dev 1.7.1+dfsg1-2ubuntu1.
This file is owned by root:root, with mode 0o755.
..
/usr/include/viennacl/linalg/detail/amg/
/usr/include/viennacl/linalg/detail/amg/amg_base.hpp
/usr/include/viennacl/linalg/detail/bisect/
/usr/include/viennacl/linalg/detail/bisect/bisect_kernel_calls.hpp
/usr/include/viennacl/linalg/detail/bisect/bisect_large.hpp
/usr/include/viennacl/linalg/detail/bisect/bisect_small.hpp
/usr/include/viennacl/linalg/detail/bisect/config.hpp
/usr/include/viennacl/linalg/detail/bisect/gerschgorin.hpp
/usr/include/viennacl/linalg/detail/bisect/structs.hpp
/usr/include/viennacl/linalg/detail/bisect/util.hpp
/usr/include/viennacl/linalg/detail/ilu/
/usr/include/viennacl/linalg/detail/ilu/block_ilu.hpp
/usr/include/viennacl/linalg/detail/ilu/chow_patel_ilu.hpp
/usr/include/viennacl/linalg/detail/ilu/common.hpp
/usr/include/viennacl/linalg/detail/ilu/ilu0.hpp
/usr/include/viennacl/linalg/detail/ilu/ilut.hpp
/usr/include/viennacl/linalg/detail/op_applier.hpp
/usr/include/viennacl/linalg/detail/op_executor.hpp
/usr/include/viennacl/linalg/detail/spai/
/usr/include/viennacl/linalg/detail/spai/block_matrix.hpp
/usr/include/viennacl/linalg/detail/spai/block_vector.hpp
/usr/include/viennacl/linalg/detail/spai/fspai.hpp
/usr/include/viennacl/linalg/detail/spai/qr.hpp
/usr/include/viennacl/linalg/detail/spai/small_matrix.hpp
/usr/include/viennacl/linalg/detail/spai/spai-dynamic.hpp
/usr/include/viennacl/linalg/detail/spai/spai-static.hpp
/usr/include/viennacl/linalg/detail/spai/spai.hpp
/usr/include/viennacl/linalg/detail/spai/spai_tag.hpp
/usr/include/viennacl/linalg/detail/spai/sparse_vector.hpp