The ARM Neon stuff is needed for ARM64, too (iOS at least)

Not sure why the code has now started to require that, even if have
used the same bundled libpng as for a long time.

Change-Id: I2da223bc46c24563ce9d170643c28cc5c93f7d56

external/libpng/StaticLibrary_libpng.mk

@@ -33,7 +33,7 @@ $(eval $(call gb_StaticLibrary_add_generated_cobjects,libpng,\
 	UnpackedTarball/libpng/pngwrite \
 	UnpackedTarball/libpng/pngwtran \
 	UnpackedTarball/libpng/pngwutil \
-	$(if $(filter ARM,$(CPUNAME)),\
+	$(if $(filter ARM ARM64,$(CPUNAME)),\
 	    UnpackedTarball/libpng/arm/arm_init \
 	    UnpackedTarball/libpng/arm/filter_neon_intrinsics \
 	) \