build: downgrade NDK to r21e and added macOS Android build support

[ErikBjare]

We briefly had working builds for r25 (6f1d5b2), but they started failing with a weird:

  = note: ld: error: unable to find library -lgcc
          clang-14: error: linker command failed with exit code 1 (use -v to see invocation)

This change works locally for me (on macOS), hoping it fixes CI too.

[codecov]

Codecov Report

Base: 72.83% // Head: 72.83% // No change to project coverage 👍

Coverage data is based on head (9bfbb14) compared to base (8bf4cb3).
Patch has no changes to coverable lines.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #325   +/-   ##
=======================================
  Coverage   72.83%   72.83%           
=======================================
  Files          45       45           
  Lines        2790     2790           
=======================================
  Hits         2032     2032           
  Misses        758      758           

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[ShootingKing-AM]

Lets update the ndk at a later moment, lgcc is removed in newer version of NDK lgcc exports are available in lunwind but that is not known to upstream crates (also this is specific to android-ndk-toolkit) (and many more changes need to done if we update ndk now)

The fix is making a file gcc.a file redirect to lunwind internally as mentioned in this comment rust-lang/rust#85806 (comment)

aw-android(and android relevant in aw-server-rust) are little old in updates, we can do this update later (have to update ci etc etc..). But I feel its better to make a working aw-android build with existing code with minimal changes(so that it can be functionally built as of today) as in #323 and ActivityWatch/aw-android#85; then we can pull remaining dependencies including ndk to latest.

[ErikBjare]

@ShootingKing-AM That is great info, thanks!

Working on ActivityWatch/aw-android#87, which should hopefully give a working build, and then we can then use your E2E PR to test it fully :)