libpixman does not propagate universal to libpng

[gary.verhaegen@…]

While trying to get firefox-x11 to compile, I first tried to compile it with a normal port install on a clean system, which installed all the dependencies in x86_64 format. As it did not work, I then tried a port install firefox-x11 build_arch=i386, which first proceeded by recursively reinstalling all dependencies with the universal flag. The libpixman build failed at the linking stage stating that it could not find some symbols for the i386 architecture; it turns out that it had not reinstalled the libpng port with the universal variant. Doing it manually solved the problem and allowed libpixman to finish. I'm guessing it should be a pretty simple fix in the portfile.

[ryandesign (Ryan Carsten Schmidt)]

Duplicate of #32260.