setupext.patch

--- setupext.py
+++ setupext.py
@@ -998,7 +998,7 @@ class Png(SetupPackage):
             ]
         ext = make_extension('matplotlib._png', sources)
         pkg_config.setup_extension(
-            ext, 'libpng', default_libraries=['png', 'z'],
+            ext, 'libpng', default_libraries=['libpng', 'z'],
             alt_exec='libpng-config --ldflags')
         Numpy().add_flags(ext)
         return ext