[tlbuild] Allow for building synctex as shared library

[Karl Berry]

    Didn't realize that the tlbuild list removes cc's.

The list does not "remove" anything.  It is a standard mailman list set
up in the same way as any other on tug.org (and most on gnu.org, etc.),
with reply-to = poster.

What is necessary is for people to use "reply to all" instead of just
"reply".

(I have explicitly removed the @bugs.debian.org address from the cc list
for this message, the list did not do it. :)

karl