[io] Prevent losing data due to SIGTERM (under Unix)

[ferdymercury]

This Pull request:

Changes or fixes:

Fixes #13300

• I tested this locally on Ubu22 and it works fine.
• I do not know how to properly test it using GTEST, I only found test_polling.cxx doing something like that but it looked too complicated, so I ended up simplifying.
• I do not know if Windows must catch SIGTERM somewhere else @bellenot ?

Checklist:

• tested changes locally
• updated the docs (if necessary)

[github-actions]

Test Results

    17 files      17 suites   4d 10h 19m 4s ⏱️
 2 738 tests  2 737 ✅ 0 💤 1 ❌
44 943 runs  44 942 ✅ 0 💤 1 ❌

For more details on these failures, see this check.

Results for commit 03f2302.

♻️ This comment has been updated with latest results.

[bellenot]

@ferdymercury The SIGILL and SIGTERM signals aren't generated under Windows. They're included for ANSI compatibility. See the signal reference