/usr/include/musicbrainz4/ is in libmusicbrainz4-dev 4.0.0-0ubuntu1.
This file is owned by root:root, with mode 0o755.
..
/usr/include/musicbrainz4/Alias.h
/usr/include/musicbrainz4/AliasList.h
/usr/include/musicbrainz4/Annotation.h
/usr/include/musicbrainz4/AnnotationList.h
/usr/include/musicbrainz4/Artist.h
/usr/include/musicbrainz4/ArtistCredit.h
/usr/include/musicbrainz4/ArtistList.h
/usr/include/musicbrainz4/Attribute.h
/usr/include/musicbrainz4/AttributeList.h
/usr/include/musicbrainz4/CDStub.h
/usr/include/musicbrainz4/CDStubList.h
/usr/include/musicbrainz4/Collection.h
/usr/include/musicbrainz4/CollectionList.h
/usr/include/musicbrainz4/Disc.h
/usr/include/musicbrainz4/DiscList.h
/usr/include/musicbrainz4/Entity.h
/usr/include/musicbrainz4/FreeDBDisc.h
/usr/include/musicbrainz4/FreeDBDiscList.h
/usr/include/musicbrainz4/HTTPFetch.h
/usr/include/musicbrainz4/ISRC.h
/usr/include/musicbrainz4/ISRCList.h
/usr/include/musicbrainz4/Label.h
/usr/include/musicbrainz4/LabelInfo.h
/usr/include/musicbrainz4/LabelInfoList.h
/usr/include/musicbrainz4/LabelList.h
/usr/include/musicbrainz4/Lifespan.h
/usr/include/musicbrainz4/List.h
/usr/include/musicbrainz4/ListImpl.h
/usr/include/musicbrainz4/Medium.h
/usr/include/musicbrainz4/MediumList.h
/usr/include/musicbrainz4/Message.h
/usr/include/musicbrainz4/Metadata.h
/usr/include/musicbrainz4/NameCredit.h
/usr/include/musicbrainz4/NameCreditList.h
/usr/include/musicbrainz4/NonMBTrack.h
/usr/include/musicbrainz4/NonMBTrackList.h
/usr/include/musicbrainz4/PUID.h
/usr/include/musicbrainz4/PUIDList.h
/usr/include/musicbrainz4/Query.h
/usr/include/musicbrainz4/Rating.h
/usr/include/musicbrainz4/Recording.h
/usr/include/musicbrainz4/RecordingList.h
/usr/include/musicbrainz4/Relation.h
/usr/include/musicbrainz4/RelationList.h
/usr/include/musicbrainz4/Release.h
/usr/include/musicbrainz4/ReleaseGroup.h
/usr/include/musicbrainz4/ReleaseGroupList.h
/usr/include/musicbrainz4/ReleaseList.h
/usr/include/musicbrainz4/Tag.h
/usr/include/musicbrainz4/TagList.h
/usr/include/musicbrainz4/TextRepresentation.h
/usr/include/musicbrainz4/Track.h
/usr/include/musicbrainz4/TrackList.h
/usr/include/musicbrainz4/UserRating.h
/usr/include/musicbrainz4/UserTag.h
/usr/include/musicbrainz4/UserTagList.h
/usr/include/musicbrainz4/Work.h
/usr/include/musicbrainz4/WorkList.h
/usr/include/musicbrainz4/mb4_c.h
/usr/include/musicbrainz4/xmlParser.h