Build libpng as part of deps on Linux
Build libpng as part of deps on Linux

- We've found counter case where the system provided one is missing or is too old.
prusa3d/Slic3r,prusa3d/Slic3r,prusa3d/Slic3r,prusa3d/Slic3r,prusa3d/Slic3r,prusa3d/Slic3r,prusa3d/Slic3r