os: freeze signals constant

Remove the ability to mutate signals constant as doing so can lead to
unexpected behavior, notably when spawning child process.

Fixes: https://github.com/nodejs/node/issues/44749
PR-URL: https://github.com/nodejs/node/pull/61038
Reviewed-By: Yagiz Nizipli <yagiz@nizipli.com>
Reviewed-By: Aviv Keller <me@aviv.sh>

lib/os.js

@@ -25,6 +25,7 @@ const {
   ArrayPrototypePush,
   Float64Array,
   ObjectDefineProperties,
+  ObjectFreeze,
   StringPrototypeSlice,
   SymbolToPrimitive,
 } = primordials;
@@ -330,6 +331,8 @@ module.exports = {
   machine: getMachine,
 };
 
+ObjectFreeze(constants.signals);
+
 ObjectDefineProperties(module.exports, {
   constants: {
     __proto__: null,

test/parallel/test-os-constants-signals.js

@@ -0,0 +1,11 @@
+'use strict';
+
+require('../common');
+const { test } = require('node:test');
+const assert = require('node:assert');
+const { constants } = require('node:os');
+
+
+test('Verify that signals constant is immutable', () => {
+  assert.throws(() => constants.signals.FOOBAR = 1337, TypeError);
+});