bug#19831: 25.0.50; Can't build emacs 25.0.5 with libpng16 support (only libpng15)

[Eli Zaretskii]

> From: torys.anderson@gmail.com (Tory S. Anderson)
> Date: Tue, 10 Feb 2015 12:57:53 -0500
> 
> 
> I have libpng16 (and 15) installed with dev files; my libpng.so points to 
> version 16. But emacs 25.0.5 refuses to work with 16. Although the config log 
> is full of references to lpng16, it seems to choose to load with lib15 (and 
> won't build with png support if I don't make v 15 available). This is 
> breaking other programs that expect to be using the latest libpng on the 
> computer.

What does this shell command display:

  libpng-config --cflags

It looks like this is what's responsible for the fact that Emacs
decides you have libpng15 installed.  So I think the way you installed
libpng16 is missing the update of libpng-config.