Update libpng.py to 1.6.56#26592

HCL-JasonR wants to merge 7 commits into

emscripten-core:mainemscripten-core/emscripten:mainfrom

HCL-TECH-SOFTWARE:libpng-to-1.6.56HCL-TECH-SOFTWARE/emscripten:libpng-to-1.6.56Copy head branch name to clipboard