The build behaviour for graphviz changes when the builder specifies concurrent
builds (e.g. -j8). In particular, the build fails. Here's the bottom bit of
output (after ./configure, up to the failure) from a pbuilder attempt (below).
Not sure if this is any help though.

I guess this is two wishlist requests: the first is to not FTBFS if -j is
specified, I guess by not supporting it. The second would be to support it ☺