build: disable V8 untrusted code mitigations

Refs: https://github.com/v8/v8/wiki/Untrusted-code-mitigations

PR-URL: #19222
Reviewed-By: Fedor Indutny <fedor.indutny@gmail.com>
Reviewed-By: Yang Guo <yangguo@chromium.org>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Benedikt Meurer <benedikt.meurer@gmail.com>
Reviewed-By: Gus Caplan <me@gus.host>
Reviewed-By: Gibson Fahnestock <gibfahn@gmail.com>

common.gypi

@@ -35,6 +35,10 @@
     # Don't bake anything extra into the snapshot.
     'v8_use_external_startup_data%': 0,
 
+    # Disable V8 untrusted code mitigations.
+    # See https://github.com/v8/v8/wiki/Untrusted-code-mitigations
+    'v8_untrusted_code_mitigations': 'false',
+
     # Some STL containers (e.g. std::vector) do not preserve ABI compatibility
     # between debug and non-debug mode.
     'disable_glibcxx_debug': 1,

test/parallel/test-v8-untrusted-code-mitigations.js

@@ -0,0 +1,18 @@
+'use strict';
+
+require('../common');
+const assert = require('assert');
+const { execFileSync } = require('child_process');
+
+// This test checks that untrusted code mitigations in V8 are disabled
+// by default.
+
+const v8Options = execFileSync(process.execPath, ['--v8-options']).toString();
+
+const untrustedFlag = v8Options.indexOf('--untrusted-code-mitigations');
+assert.notStrictEqual(untrustedFlag, -1);
+
+const nextFlag = v8Options.indexOf('--', untrustedFlag + 2);
+const slice = v8Options.substring(untrustedFlag, nextFlag);
+
+assert(slice.match(/type: bool  default: false/));