The code in ndk-build that handles pulling up LP64 API levels to 21 if needed is wrong: https://cs.android.com/android/_/android/platform/ndk/+/5539b2f17d5bdb052bd4580ab900781fb6fcaeba:build/core/setup-abi.mk;l=35;drc=cf5442c13a4cd0fe8b01e27de3850727007988f0

subst acts on any substring, ignoring word boundaries, so 30 is "pulled up" to 210.

r21 will support API 30, so triaging for r21b.