[tlbuild] build of new dvisvgm fails

[Karl Berry]

    Ok your system, which distribution package contains that library?

glibc package has libdl.so etc. But also the dlsym/etc. symbols are
usually defined in glibc itself.

    Maybe it's needs to be installed separately?

Not likely :).

In short, current source works on rocky9 (karl at home). (I'll double check.)
Fails on alma8 (tug).
Fails on centos7 (gh).

Presumably something changed in how dvisvgm-3.2 (vs. earlier versions)
does its dl stuff, since that's why it would be failing now.

Unfortunately I won't be able to track this down today.

Martin, if you have any ideas about where to look along these lines,
that would be great :). --thanks, karl.