Add support for Apple tvOS builds

[matszczygiel]

Description of changes:

This PR makes it possible to build aws-lc-rs for Apple tvOS platform. The compilation works out of the box with only some defines missing.

Testing:

I've tested the build for aarch64-apple-tvos platform.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license and the ISC license.

[justsmth]

Thanks for the PR!

Do you know whether it would be possible to build for Apple tvOS in the GitHub CI? If so, I can add myself a backlog task to set it up.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 92.39%. Comparing base (c358484) to head (66f8efb).
Report is 234 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #848      +/-   ##
==========================================
- Coverage   95.80%   92.39%   -3.41%     
==========================================
  Files          61       71      +10     
  Lines        8143     9065     +922     
  Branches        0     9065    +9065     
==========================================
+ Hits         7801     8376     +575     
- Misses        342      423      +81     
- Partials        0      266     +266     

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[matszczygiel]

@justsmth I believe it should work as any other Apple cross-compilation job with the following differences:

• it requires nightly toolchain
• the build command is slightly different cargo +nightly build -Zbuild-std --target aarch64-apple-tvos