/usr/include/tcl8.4/tcl-private/ is in tcl8.4-dev 8.4.20-7.
This file is owned by root:root, with mode 0o755.
..
/usr/include/tcl8.4/tcl-private/compat/
/usr/include/tcl8.4/tcl-private/compat/dirent.h
/usr/include/tcl8.4/tcl-private/compat/dirent2.h
/usr/include/tcl8.4/tcl-private/compat/dlfcn.h
/usr/include/tcl8.4/tcl-private/compat/float.h
/usr/include/tcl8.4/tcl-private/compat/limits.h
/usr/include/tcl8.4/tcl-private/compat/stdlib.h
/usr/include/tcl8.4/tcl-private/compat/string.h
/usr/include/tcl8.4/tcl-private/compat/tclErrno.h
/usr/include/tcl8.4/tcl-private/compat/unistd.h
/usr/include/tcl8.4/tcl-private/generic/
/usr/include/tcl8.4/tcl-private/generic/regcustom.h
/usr/include/tcl8.4/tcl-private/generic/regerrs.h
/usr/include/tcl8.4/tcl-private/generic/regex.h
/usr/include/tcl8.4/tcl-private/generic/regguts.h
/usr/include/tcl8.4/tcl-private/generic/tcl.h
/usr/include/tcl8.4/tcl-private/generic/tclCompile.h
/usr/include/tcl8.4/tcl-private/generic/tclDecls.h
/usr/include/tcl8.4/tcl-private/generic/tclIO.h
/usr/include/tcl8.4/tcl-private/generic/tclInitScript.h
/usr/include/tcl8.4/tcl-private/generic/tclInt.h
/usr/include/tcl8.4/tcl-private/generic/tclIntDecls.h
/usr/include/tcl8.4/tcl-private/generic/tclIntPlatDecls.h
/usr/include/tcl8.4/tcl-private/generic/tclMath.h
/usr/include/tcl8.4/tcl-private/generic/tclPlatDecls.h
/usr/include/tcl8.4/tcl-private/generic/tclPort.h
/usr/include/tcl8.4/tcl-private/generic/tclRegexp.h
/usr/include/tcl8.4/tcl-private/unix/
/usr/include/tcl8.4/tcl-private/unix/tclUnixPort.h
/usr/include/tcl8.4/tcl-private/unix/tclUnixThrd.h