(for the record - I am maintainer of Tcl module, but you should use tcltk at perl dot org mailing list for problems using the module)

unfortunately the logic of Makefile.PL is twisted - I was always against making it complicated
but it grows by adding more and more include paths from different $^O variants.

You can use --include=/your/path/to/tcl/include-files to specify those, but even better is to --usestubs on linux, because this portion of makefile.pl is not broken. So try following command line:

perl Makefile.PL --usestubs
[download]

I guess this Makefile.PL needs serious cleaning upon next release.

HTH,
Vadim.