tcl: Update to version 8.6.12

tcl: Update to version 8.6.12

- Update from 8.6.11 to 8.6.12
- Update of rootfile
- Changelog is no longer supported by tcl. All changes are put into a timeline which can
   be viewed at https://core.tcl-lang.org/tcl/timeline although I can't figure out from
   the timeline what change goes with what version. Hopefully other people are better
   able to understand the information. This timelien cannot be easily summarised or
   copied into this commit.

Signed-off-by: Adolf Belka <adolf.belka@ipfire.org>
Reviewed-by: Michael Tremer <michael.tremer@ipfire.org>