Add ARM NDK to Github Actions matrix

Add ARM NDK to Github Actions matrix

- set the variable only for the required tests to keep simple the yml file
- use NDK 21.x until will be fixed the Stockfish static build problem
  with NDK 23.x
- set the test for armv7, armv7-neon, armv8 builds:
  - use armv7a-linux-androideabi21-clang++ compiler for armv7 armv7-neon
  - enforce a static build
  - silence the Warning for the unused compilation flag "-pie" with
    the static build, otherwise the Github workflow stops
  - use qemu to bench the build and get the signature

Many thanks to @pschneider1968 that made all the hard work with NDK :)

closes https://github.com/official-stockfish/Stockfish/pull/3924

No functional change