Merge branch 'jk/graph-c-expose-symbols-for-cgit' into maint

In the v1.8.0 era, we changed symbols that do not have to be global
to file scope static, but a few functions in graph.c were used by
CGit from sideways bypassing the entry points of the API the
in-tree users use.

* jk/graph-c-expose-symbols-for-cgit:
  Revert "graph.c: mark private file-scope symbols as static"