/usr/include/liboil-0.3/liboil/ is in liboil0.3-dev 0.3.17-2ubuntu4.
This file is owned by root:root, with mode 0o755.
..
/usr/include/liboil-0.3/liboil/liboil-stdint.h
/usr/include/liboil-0.3/liboil/liboil.h
/usr/include/liboil-0.3/liboil/liboilclasses.h
/usr/include/liboil-0.3/liboil/liboilcpu.h
/usr/include/liboil-0.3/liboil/liboildebug.h
/usr/include/liboil-0.3/liboil/liboilfault.h
/usr/include/liboil-0.3/liboil/liboilfuncs.h
/usr/include/liboil-0.3/liboil/liboilfunction.h
/usr/include/liboil-0.3/liboil/liboilgcc.h
/usr/include/liboil-0.3/liboil/liboilinternal.h
/usr/include/liboil-0.3/liboil/liboilparameter.h
/usr/include/liboil-0.3/liboil/liboilprofile.h
/usr/include/liboil-0.3/liboil/liboilprototype.h
/usr/include/liboil-0.3/liboil/liboilrandom.h
/usr/include/liboil-0.3/liboil/liboiltest.h
/usr/include/liboil-0.3/liboil/liboiltypes.h
/usr/include/liboil-0.3/liboil/liboilutils.h