wget -c http://downloads.sourceforge.net/project/tcl/Tcl/8.6.10/tcl8.6.10-src.tar.gz
tar -xzf tcl8.6.10-src.tar.gz
cd tcl8.6.10
mkdir -p build
cd build
../unix/configure --prefix="/usr"
make # Doesn't mind -j#
make install
ln -f -s tclsh8.6 /usr/bin/tclsh