Freetype doesnt load bitmap emojis

when trying to load noto emoji fonts, it works on desktop but not android. More specifically `FT_Load_Glyph` will return `FT_Err_Unimplemented_Feature`. I thought maybe this was due to lacking PNG support in the bundled version, so on my local copy I've uncommented `#define FT_CONFIG_OPTION_USE_PNG` in `freetype2/include/freetype/config/ftoption.h` and then add `libpng-sys = { git = "https://github.com/kornelski/rust-libpng-sys", features = ["static-libz", "static" ] }` to my `Cargo.toml`. But this hasn't fixed it. Any ideas what's missing?