/usr/include/ is in inspircd-dev 2.0.20-5build2.
This file is owned by root:root, with mode 0o755.
..
/usr/include/inspircd/
/usr/include/inspircd/ctables.h
/usr/include/inspircd/threadengines/
/usr/include/inspircd/threadengines/threadengine_win32.h
/usr/include/inspircd/threadengines/threadengine_pthread.h
/usr/include/inspircd/inspstring.h
/usr/include/inspircd/logger.h
/usr/include/inspircd/users.h
/usr/include/inspircd/numerics.h
/usr/include/inspircd/inspircd.h
/usr/include/inspircd/commands/
/usr/include/inspircd/commands/cmd_whowas.h
/usr/include/inspircd/exitcodes.h
/usr/include/inspircd/base.h
/usr/include/inspircd/configreader.h
/usr/include/inspircd/consolecolors.h
/usr/include/inspircd/threadengine.h
/usr/include/inspircd/bancache.h
/usr/include/inspircd/dynamic.h
/usr/include/inspircd/command_parse.h
/usr/include/inspircd/hashcomp.h
/usr/include/inspircd/membership.h
/usr/include/inspircd/inspircd_version.h
/usr/include/inspircd/protocol.h
/usr/include/inspircd/filelogger.h
/usr/include/inspircd/typedefs.h
/usr/include/inspircd/usermanager.h
/usr/include/inspircd/uid.h
/usr/include/inspircd/channels.h
/usr/include/inspircd/dns.h
/usr/include/inspircd/cull_list.h
/usr/include/inspircd/modes/
/usr/include/inspircd/modes/umode_o.h
/usr/include/inspircd/modes/cmode_o.h
/usr/include/inspircd/modes/cmode_l.h
/usr/include/inspircd/modes/cmode_k.h
/usr/include/inspircd/modes/cmode_v.h
/usr/include/inspircd/modes/cmode_b.h
/usr/include/inspircd/modes/umode_s.h
/usr/include/inspircd/modes/simplemodes.h
/usr/include/inspircd/inspircd_config.h
/usr/include/inspircd/snomasks.h
/usr/include/inspircd/extensible.h
/usr/include/inspircd/xline.h
/usr/include/inspircd/modules.h
/usr/include/inspircd/socketengine.h
/usr/include/inspircd/socket.h
/usr/include/inspircd/hash_map.h
/usr/include/inspircd/configparser.h
/usr/include/inspircd/inspsocket.h
/usr/include/inspircd/timer.h
/usr/include/inspircd/caller.h
/usr/include/inspircd/mode.h
/usr/include/inspircd/testsuite.h