Signals

[rennergade]

Description

PR mostly via @jesings but with my help and some help from @AlpacaMax

Fixes # (issue) This PR adds signal handling through extensive changes to the signal runtime.

In depth explanation for these changes can be found in the extensive documentation at the top of nacl_signal.c and nacl_syscal_64.S

This PR also adds hooks for sigaction, sigprocmask, and kill.

Type of change

• [x] New feature (non-breaking change which adds functionality)
• [x] Breaking change (fix or feature that would cause existing functionality to not work as expected)
• [x] This change requires a documentation update

How Has This Been Tested?

WARNING: test suite will fail due to cross-repo PR Tests in lind_project Postgres/LAMP

Checklist:

• [ ] My code follows the style guidelines of this project
• [x] I have commented my code, particularly in hard-to-understand areas
• [x] My changes generate no new warnings
• [x] I have added tests that prove my fix is effective or that my feature works
• [x] Any dependent changes have been added to a pull request and/or merged in other modules (lind-project, lind-glibc, safeposix-rust)

[yzhang71]

make[1]: *** [Makefile:20: lind/nacl] Error 1 make[1]: Leaving directory '/home/lind/lind_project/actions-runner/_work/native_client/native_client' make: *** [Makefile:17: nacl] Error 2 Error: Process completed with exit code 2. There are some errors in the make process.

[rennergade]

@yzhang71 I think your refactoring comments are valid but these things appear throughout the whole file and are kind of standard at this point, fixing all that would be a separate PR most likely