[v2] fix: use unix signal handlers instead of Mach ports

[Stebalien]

This will apparently interfere with some debugging tools, but we ran into an issue where Mach ports weren't always catching illegal instruction signals form wasmtime (affecting macos only).

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 37.93%. Comparing base (4777600) to head (54b2e60).

Additional details and impacted files

@@              Coverage Diff               @@
##           release/v2    #2042      +/-   ##
==============================================
+ Coverage       31.86%   37.93%   +6.06%     
==============================================
  Files              83       43      -40     
  Lines            6459     1827    -4632     
==============================================
- Hits             2058      693    -1365     
+ Misses           4401     1134    -3267     

see 46 files with indirect coverage changes