/usr/include/postgresql/9.5/server/parser/ is in postgresql-server-dev-9.5 9.5.2-1.
This file is owned by root:root, with mode 0o755.
..
/usr/include/postgresql/9.5/server/parser/analyze.h
/usr/include/postgresql/9.5/server/parser/gram.h
/usr/include/postgresql/9.5/server/parser/gramparse.h
/usr/include/postgresql/9.5/server/parser/keywords.h
/usr/include/postgresql/9.5/server/parser/kwlist.h
/usr/include/postgresql/9.5/server/parser/parse_agg.h
/usr/include/postgresql/9.5/server/parser/parse_clause.h
/usr/include/postgresql/9.5/server/parser/parse_coerce.h
/usr/include/postgresql/9.5/server/parser/parse_collate.h
/usr/include/postgresql/9.5/server/parser/parse_cte.h
/usr/include/postgresql/9.5/server/parser/parse_expr.h
/usr/include/postgresql/9.5/server/parser/parse_func.h
/usr/include/postgresql/9.5/server/parser/parse_node.h
/usr/include/postgresql/9.5/server/parser/parse_oper.h
/usr/include/postgresql/9.5/server/parser/parse_param.h
/usr/include/postgresql/9.5/server/parser/parse_relation.h
/usr/include/postgresql/9.5/server/parser/parse_target.h
/usr/include/postgresql/9.5/server/parser/parse_type.h
/usr/include/postgresql/9.5/server/parser/parse_utilcmd.h
/usr/include/postgresql/9.5/server/parser/parser.h
/usr/include/postgresql/9.5/server/parser/parsetree.h
/usr/include/postgresql/9.5/server/parser/scanner.h
/usr/include/postgresql/9.5/server/parser/scansup.h