Support same android ndk versions as rust-lang/rust and rust-lang/libc

[gnzlbg]

cross currently targets android ndk version 21. The following versions are targeted by Rust and libc:

• rust-lang/rust:

  • arm-android: NDK arm 15c
  • armv7-android: NDK arm 14
  • aarch64-android: NDK arm64 21

• rust-lang/libc:

  • arm-android: NDK arm 15b
  • armv7-android: NDK arm 15b
  • aarch64-android: NDK arm64 15b

It would be nice if we could add an option to cross to let users specify the android NDK version. Or if we would at least support two different NDK versions natively (e.g. by providing docker images for both): latest (e.g. version 21), and rustc (same versions as rust-lang/rust).

This would be a pre-requisite for using cross as the testing framework for libc and other rust-lang /rust-lang-nursery components like stdsimd, jemallocator, etc.

[flxo]

@gnzlbg Where can I find the exact Android/NDK API levels used by Rust and libc?

[flxo]

I found in the libc CI a hint that master currently uses r21d and API level 28.