This tk update (version 8.6.10) provides new tk library named libtk8.6.so
along with other files which includes development header files as well.
It also provides older library "libtk8.4.so" so that the existing applications
linking to the older library should not get broken. The unversioned library
libtk.so is still a symbolic link to the older library for the same reason
mentioned above. Users are recommended to link their new applications
or want to recompile the existing applications to link to libtk8.6.so(-ltk8.6).
Please check /usr/lib/tkConfig.sh for correct build and linker flags.