/usr/include/clc/relational/ is in libclc-dev 0.2.0+git20180312-1.
This file is owned by root:root, with mode 0o755.
..
/usr/include/clc/relational/all.h
/usr/include/clc/relational/any.h
/usr/include/clc/relational/binary_decl.inc
/usr/include/clc/relational/bitselect.h
/usr/include/clc/relational/bitselect.inc
/usr/include/clc/relational/floatn.inc
/usr/include/clc/relational/isequal.h
/usr/include/clc/relational/isfinite.h
/usr/include/clc/relational/isgreater.h
/usr/include/clc/relational/isgreaterequal.h
/usr/include/clc/relational/isinf.h
/usr/include/clc/relational/isless.h
/usr/include/clc/relational/islessequal.h
/usr/include/clc/relational/islessgreater.h
/usr/include/clc/relational/isnan.h
/usr/include/clc/relational/isnormal.h
/usr/include/clc/relational/isnotequal.h
/usr/include/clc/relational/isordered.h
/usr/include/clc/relational/isunordered.h
/usr/include/clc/relational/select.h
/usr/include/clc/relational/select.inc
/usr/include/clc/relational/signbit.h
/usr/include/clc/relational/unary_decl.inc