fix: use process signal numbers from correct architecture

[Garmelon]

This PR fixes some process signals that were incorrectly numbered.

From what I can tell, the code used signals and signal numbers for Alpha/SPARC, not x86/ARM. The test was also broken and always green, hiding the mistake.

[mathlib-lean-pr-testing]

Mathlib CI status (docs):

• ❗ Batteries/Mathlib CI will not be attempted unless your PR branches off the nightly-with-mathlib branch. Try git rebase 47833725eaded4cec8cc7944ab656eaf05208da7 --onto e8048291010c815d0d30926924e7ad7afc18b1c0. You can force Mathlib CI using the force-mathlib-ci label. (2026-03-12 19:21:19)
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• ❗ Batteries/Mathlib CI will not be attempted unless your PR branches off the nightly-with-mathlib branch. Try git rebase 49715fe63cf9181114c3dafc94f1b8490af41276 --onto 6714601ee4a123fef0f6ff3e44f01086ba78dfce. You can force Mathlib CI using the force-mathlib-ci label. (2026-03-17 14:02:20)

[leanprover-bot]

Reference manual CI status:

• ❗ Reference manual CI will not be attempted unless your PR branches off the nightly-with-manual branch. Try git rebase 47833725eaded4cec8cc7944ab656eaf05208da7 --onto 24acf2b895670fdeeafc64c4f606e7a0ebc19e6d. You can force reference manual CI using the force-manual-ci label. (2026-03-12 19:21:21)
• ❗ Reference manual CI will not be attempted unless your PR branches off the nightly-with-manual branch. Try git rebase 49715fe63cf9181114c3dafc94f1b8490af41276 --onto cfa8c5a036d6990635c6ec50b02d0e806995cec3. You can force reference manual CI using the force-manual-ci label. (2026-03-16 18:41:19)

[algebraic-dev]

Maybe we should remove the toInt32 function and perform the translation on the C++ side using the constants, since the code needs to run on multiple operating systems and architectures, just to make sure it works correctly every time. What do you think? I also think that the behavior between your branch and the master branch differs on MacOS for this code:

def main : IO Unit := Async.block do
  let waiter ← Signal.Waiter.mk .sigusr1 false
  IO.println "Waiting for SIGUSR1..."
  discard <| await (← waiter.wait)
  IO.println "Received SIGUSR1!"

In macOS the master branch captures the signal, in your branch it just kills the process.

[Garmelon]

Would something like this work? I don't have a mac to test against.

[algebraic-dev]

It works on macOS now.

[Garmelon]

I think the test is flaky when other tests are running in parallel