libpng dependency issue

[Vincent Povirk]

> As a side note, you need to do a similar work on winemenubuilder, as it uses
> libpng and fails linking without modifications. to test this images i
> statically linked it to libpng, just to make it work, as it wasn't needed in
> your test.
> Thank you for working on this, since i'm not really an expert on this
> dynamical loading code and couldn't help.

Technically, winemenubuilder should be using windowscodecs for its png
support, like the rest of wine. I believe Steven Edwards has done some
work on this.