os: make EOL configurable and readonly

Refs: #14619

lib/os.js

@@ -140,7 +140,6 @@ function networkInterfaces() {
 module.exports = exports = {
   arch,
   cpus,
-  EOL: isWindows ? '\r\n' : '\n',
   endianness,
   freemem: getFreeMem,
   homedir: getHomeDirectory,
@@ -162,8 +161,17 @@ module.exports = exports = {
   tmpDir: deprecate(tmpdir, tmpDirDeprecationMsg, 'DEP0022')
 };
 
-Object.defineProperty(module.exports, 'constants', {
-  configurable: false,
-  enumerable: true,
-  value: constants
+Object.defineProperties(module.exports, {
+  constants: {
+    configurable: false,
+    enumerable: true,
+    value: constants
+  },
+
+  EOL: {
+    configurable: true,
+    enumerable: true,
+    writable: false,
+    value: isWindows ? '\r\n' : '\n'
+  }
 });

test/parallel/test-os-eol.js

@@ -0,0 +1,27 @@
+'use strict';
+
+const common = require('../common');
+const assert = require('assert');
+const os = require('os');
+
+const eol = common.isWindows ? '\r\n' : '\n';
+
+assert.strictEqual(os.EOL, eol);
+
+common.expectsError(function() {
+  os.EOL = 123;
+}, {
+  type: TypeError,
+  message: /^Cannot assign to read only property 'EOL' of object '#<Object>'$/
+});
+
+const foo = 'foo';
+Object.defineProperties(os, {
+  EOL: {
+    configurable: true,
+    enumerable: true,
+    writable: false,
+    value: foo
+  }
+});
+assert.strictEqual(os.EOL, foo);