[tlbuild] building for distribution with shared breaks in dvisvgm

[Karl Berry]

    be set automatically unless overriden on the commandline of configure,
    independently from --disable-texlive-native-build.

I do nothing with --enable-bundled-libs. If you specify it, I thought it
would get passed down everywhere. The AC_ARG_ENABLE in
dvisvgm/configure.ac is still there. (Indeed, I tried to minimize the
differences between tl's and upstreams configure.ac.)

Meanwhile, I had another idea: what if, as a Debian patch, you 
reverted dvisvgm/configure.ac to dvisvgm-src/configure.ac,
and dvisvgm-src/Makefile.am to the original (if desired -- just recurses
  into tests and doc subdirs, which we don't want for TL),
and dvisvgm-src/src/Makefile.am to the original (definitely).

You can see the changes I made for TL in
dvisvgm/TLpatches/patch-08-makefiles, although they are not especially
comprehensible in that (or any other :) form.

If you aren't building with --enable-native-texlive, I'd expect the
upstream versions should work better for you, modulo the xxhash stuff.
(Another patch could be to treat xxhash like clipper I suppose, if you
don't want to wait until your xxhash submission is approved or whatever.)

I didn't try it ... just an idea ... -k