Graphviz Makefile uses the command "tclsh" to generate the manuals even if ./configure detected that tclsh is under a different name (say "tclsh8.4", as installed by portage). "tclsh" is hardcoded in tclpkg/gv/Makefile.am and should be changed to $(TCLSH) to avoid build errors.
Created attachment 103741 [details, diff] Replacement graphviz-2.8-notcl.patch The graphviz-2.8-notcl.patch file currently found in /usr/portage/media-gfx/graphviz/files/ can be safely replaced with this one. It contains the same changes but replaces "tclsh" with $(TCLSH) as a bonus.
/usr/bin/tclsh should be a link to tclsh-8.4. It's owned by dev-lang/tcl. If that link doesn't exist it's a problem with your install or the tcl ebuild. Please reopen if I've misunderstood the problem.
Still configure detecting one executable and the build process using another one sounds like a bug to me, even if it should not affect Gentoo. It might be a good idea to report this issue upstream.
