qrencode: fix pkgconfig location.
qrencode: fix pkgconfig location.

* explicitly link against libpng16

miqlas/haikuports,nielx/haikuports,moochris/haikuports,koletzky/haikuports,moochris/haikuports,haikuports/haikuports,nielx/haikuports,koletzky/haikuports,nielx/haikuports,haikuports/haikuports,Begasus/haikuports,haikuports/haikuports,koletzky/haikuports,miqlas/haikuports,Begasus/haikuports,haikuports/haikuports,moochris/haikuports,Begasus/haikuports,Begasus/haikuports,haikuports/haikuports,Begasus/haikuports,miqlas/haikuports