$ wget https://prdownloads.sourceforge.net/tcl/tk8.6.10-src.tar.gz
$ tar xvf tk8.6.10-src.tar.gz
$ cd tk8.6.10/unix/
$ mkdir build
$ cd build
$ ../configure --prefix=/opt/tcl/8.6.10 --enable-threads --enable-shared --with-tcl=/opt/tcl/8.6.10/lib
$