Patch is trivial - present in the upstream bug.
For the moment, configure.ac will need adding libpng15 in the obvious place.
Quite fortunately, once released, gtk-pixbuf 2.24.0 will move libpng to Requires.private, so the headache will be even smaller.
*** Bug 355871 has been marked as a duplicate of this bug. ***
vapier's build.log with libpng 1.5.x is here:
ugh, typo in summary makes it hard for searches to hit
This is the commit:
Fixed in the tree, thanks for reporting.