[tlbuild] --disable-dvisvgm avoids configure

[Karl Berry]

    what's the proper command to build *just* dvisvgm?

I wrote down the basic strategy here:
http://tug.org/texlive/doc/tlbuild.html#Build-one-package

Although of course there's no need for a whole separate copy of the
sources if the two builds are going to be side by side. It would suffice
to have two separate build trees (say, Work and Work-svgm). You can do
that with ./Build or any other method, but I don't have an exact recipe
at hand.  --hope this helps, karl.