Use replace-libs for matplotlib (#1037)

The library that is supplied by USE_PNG is png, but matplotlib seeks
png16. With the fastcomp backend, we end up ignoring it anyway, but with
the upstream backend this will be the correct course of action

packages/matplotlib/meta.yaml

@@ -23,6 +23,8 @@ source:
 build:
   cflags: -s USE_FREETYPE=1 -s USE_LIBPNG=1 -s USE_ZLIB=1
   ldflags: ../../../../emsdk/emsdk/fastcomp/emscripten/cache/asmjs/libpng.bc
+  replace-libs:
+    - png16=png
   post: |
     wget -O $SITEPACKAGES/matplotlib/mpl-data/fonts/ttf/Humor-Sans.ttf http://antiyawn.com/uploads/Humor-Sans-1.0.ttf
     rm -rf $SITEPACKAGES/matplotlib/backends/qt_editor

pyodide_build/pywasmcross.py

@@ -330,7 +330,7 @@ def handle_command(line, args, dryrun=False):
             continue
 
         # See https://github.com/emscripten-core/emscripten/issues/8650
-        if arg in ["-lfreetype", "-lz", "-lpng16", "-lgfortran"]:
+        if arg in ["-lfreetype", "-lz", "-lpng", "-lgfortran"]:
             continue
 
         new_args.append(arg)