/usr/lib/llvm-6.0/include/polly/isl/ is in libclang-common-6.0-dev 1:6.0-1ubuntu2.
This file is owned by root:root, with mode 0o755.
..
/usr/lib/llvm-6.0/include/polly/isl/aff.h
/usr/lib/llvm-6.0/include/polly/isl/aff_type.h
/usr/lib/llvm-6.0/include/polly/isl/arg.h
/usr/lib/llvm-6.0/include/polly/isl/ast.h
/usr/lib/llvm-6.0/include/polly/isl/ast_build.h
/usr/lib/llvm-6.0/include/polly/isl/ast_type.h
/usr/lib/llvm-6.0/include/polly/isl/band.h
/usr/lib/llvm-6.0/include/polly/isl/constraint.h
/usr/lib/llvm-6.0/include/polly/isl/ctx.h
/usr/lib/llvm-6.0/include/polly/isl/deprecated/
/usr/lib/llvm-6.0/include/polly/isl/deprecated/aff_int.h
/usr/lib/llvm-6.0/include/polly/isl/deprecated/ast_int.h
/usr/lib/llvm-6.0/include/polly/isl/deprecated/constraint_int.h
/usr/lib/llvm-6.0/include/polly/isl/deprecated/ilp_int.h
/usr/lib/llvm-6.0/include/polly/isl/deprecated/int.h
/usr/lib/llvm-6.0/include/polly/isl/deprecated/map_int.h
/usr/lib/llvm-6.0/include/polly/isl/deprecated/mat_int.h
/usr/lib/llvm-6.0/include/polly/isl/deprecated/point_int.h
/usr/lib/llvm-6.0/include/polly/isl/deprecated/polynomial_int.h
/usr/lib/llvm-6.0/include/polly/isl/deprecated/set_int.h
/usr/lib/llvm-6.0/include/polly/isl/deprecated/union_map_int.h
/usr/lib/llvm-6.0/include/polly/isl/deprecated/val_int.h
/usr/lib/llvm-6.0/include/polly/isl/deprecated/vec_int.h
/usr/lib/llvm-6.0/include/polly/isl/flow.h
/usr/lib/llvm-6.0/include/polly/isl/hash.h
/usr/lib/llvm-6.0/include/polly/isl/hmap.h
/usr/lib/llvm-6.0/include/polly/isl/id.h
/usr/lib/llvm-6.0/include/polly/isl/id_to_ast_expr.h
/usr/lib/llvm-6.0/include/polly/isl/id_to_id.h
/usr/lib/llvm-6.0/include/polly/isl/id_to_pw_aff.h
/usr/lib/llvm-6.0/include/polly/isl/ilp.h
/usr/lib/llvm-6.0/include/polly/isl/isl-noexceptions.h
/usr/lib/llvm-6.0/include/polly/isl/list.h
/usr/lib/llvm-6.0/include/polly/isl/local_space.h
/usr/lib/llvm-6.0/include/polly/isl/lp.h
/usr/lib/llvm-6.0/include/polly/isl/map.h
/usr/lib/llvm-6.0/include/polly/isl/map_to_basic_set.h
/usr/lib/llvm-6.0/include/polly/isl/map_type.h
/usr/lib/llvm-6.0/include/polly/isl/mat.h
/usr/lib/llvm-6.0/include/polly/isl/maybe.h
/usr/lib/llvm-6.0/include/polly/isl/maybe_ast_expr.h
/usr/lib/llvm-6.0/include/polly/isl/maybe_basic_set.h
/usr/lib/llvm-6.0/include/polly/isl/maybe_id.h
/usr/lib/llvm-6.0/include/polly/isl/maybe_pw_aff.h
/usr/lib/llvm-6.0/include/polly/isl/maybe_templ.h
/usr/lib/llvm-6.0/include/polly/isl/multi.h
/usr/lib/llvm-6.0/include/polly/isl/obj.h
/usr/lib/llvm-6.0/include/polly/isl/options.h
/usr/lib/llvm-6.0/include/polly/isl/point.h
/usr/lib/llvm-6.0/include/polly/isl/polynomial.h
/usr/lib/llvm-6.0/include/polly/isl/polynomial_type.h
/usr/lib/llvm-6.0/include/polly/isl/printer.h
/usr/lib/llvm-6.0/include/polly/isl/printer_type.h
/usr/lib/llvm-6.0/include/polly/isl/schedule.h
/usr/lib/llvm-6.0/include/polly/isl/schedule_node.h
/usr/lib/llvm-6.0/include/polly/isl/schedule_type.h
/usr/lib/llvm-6.0/include/polly/isl/set.h
/usr/lib/llvm-6.0/include/polly/isl/set_type.h
/usr/lib/llvm-6.0/include/polly/isl/space.h
/usr/lib/llvm-6.0/include/polly/isl/stdint.h
/usr/lib/llvm-6.0/include/polly/isl/stream.h
/usr/lib/llvm-6.0/include/polly/isl/union_map.h
/usr/lib/llvm-6.0/include/polly/isl/union_map_type.h
/usr/lib/llvm-6.0/include/polly/isl/union_set.h
/usr/lib/llvm-6.0/include/polly/isl/union_set_type.h
/usr/lib/llvm-6.0/include/polly/isl/val.h
/usr/lib/llvm-6.0/include/polly/isl/val_gmp.h
/usr/lib/llvm-6.0/include/polly/isl/vec.h
/usr/lib/llvm-6.0/include/polly/isl/version.h
/usr/lib/llvm-6.0/include/polly/isl/vertices.h