[tlbuild] dvisvgm link errors when building with --with-system-libgs

[Karl Berry]

Hi Paul - if you're building within TL, I removed all the libgs
configure options, as far as I know, so --with[out]-system-libgs should
have no effect. If it is anyway, I can't explain why, can you check into
it further? (See lines 56ff. of texk/dvisvgm/configure.acl)

Instead, in TL, libgs is (supposed to be) forced to be loaded at runtime
with libdl, and not included at link time. Any other method creates a
binary that is not likely to work on any system other than the
builder's.

For any other case, it seems better to me to build Martin's original
source (ctan.org/pkg/dvisvgm), which does try to link against libgs on
the current system, than what is in TL, and issues should go to him :).
That logic is texk/dvisvgm/dvisvgm-src/configure.ac, lines
68ff. (That configure file is not used at all in TL.)

Best,
Karl