tcl: disable for static builds

After discussion on mailing list...

http://lists.busybox.net/pipermail/buildroot/2015-March/121198.html



...we decided to disable tcl for static builds and let someone
interested on it to do the needed changes to add support for static
builds.

Signed-off-by: Vicente Olivert Riera <Vincent.Riera@imgtec.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>