feat: enable TCC JIT on macOS

[esrrhs]

Summary

• Enable TCC JIT tests on macOS now that arm64 ABI compatibility issues have been fixed
• Add executable permission to build scripts (bison/build.sh, flex/build.sh)

Context

Previously, TCC JIT was disabled on macOS due to arm64 codegen issues. After the fixes in commits c9d3532 (arm64 ABI compatibility) and 384be54 (CVar POD for arm64 ABI), TCC JIT should now work correctly on macOS.

Test plan

• Verify macOS CI passes with TCC JIT tests enabled
• Confirm all unit tests pass on Linux (verified locally: 411 tests passed)

🤖 Generated with Claude Code

[codecov-commenter]

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Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.80%. Comparing base (cab78d0) to head (647d2c5).
⚠️ Report is 136 commits behind head on master.
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Additional details and impacted files

@@            Coverage Diff             @@
##           master      #98      +/-   ##
==========================================
+ Coverage   96.70%   97.80%   +1.10%     
==========================================
  Files          62       67       +5     
  Lines        9198    12000    +2802     
==========================================
+ Hits         8895    11737    +2842     
+ Misses        303      263      -40     

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