Tcl/tk-8.5.0 released at December 20, and comment in /usr/portage/profiles/package.mask should be updated or that mask should be removed.
I agree, package.mask still says "Mask alpha versions"
Unmask it please
Unmasked; just 90% of stuff that depends on tcl/tk in the tree doesn't compile because noone ever checked anything before unmasking, nor did file any bugs for maintainers and now we are getting flooded by bugs from broken users. :-( *** This bug has been marked as a duplicate of bug 173467 ***