contrib: png: update to 1.6.39
One thing I'm unclear on is if NEON optimizations need to be explicitly enabled for all appropriate platforms (right now it's just ios and win32) given:
- Disabled the ARM Neon optimizations by default in the CMake file, following the default behavior of the configure script.
See: http://www.libpng.org/pub/png/src/libpng-1.6.39-README.txt
Edited by Tristan Matthews