/usr/include/msgpack/predef/os/ is in libmsgpack-dev 2.1.5-1.
This file is owned by root:root, with mode 0o755.
..
/usr/include/msgpack/predef/os/aix.h
/usr/include/msgpack/predef/os/amigaos.h
/usr/include/msgpack/predef/os/android.h
/usr/include/msgpack/predef/os/beos.h
/usr/include/msgpack/predef/os/bsd/
/usr/include/msgpack/predef/os/bsd.h
/usr/include/msgpack/predef/os/bsd/bsdi.h
/usr/include/msgpack/predef/os/bsd/dragonfly.h
/usr/include/msgpack/predef/os/bsd/free.h
/usr/include/msgpack/predef/os/bsd/net.h
/usr/include/msgpack/predef/os/bsd/open.h
/usr/include/msgpack/predef/os/cygwin.h
/usr/include/msgpack/predef/os/haiku.h
/usr/include/msgpack/predef/os/hpux.h
/usr/include/msgpack/predef/os/ios.h
/usr/include/msgpack/predef/os/irix.h
/usr/include/msgpack/predef/os/linux.h
/usr/include/msgpack/predef/os/macos.h
/usr/include/msgpack/predef/os/os400.h
/usr/include/msgpack/predef/os/qnxnto.h
/usr/include/msgpack/predef/os/solaris.h
/usr/include/msgpack/predef/os/unix.h
/usr/include/msgpack/predef/os/vms.h
/usr/include/msgpack/predef/os/windows.h