deps: V8: cherry-pick 8ec2651fbdd8

Original commit message:

    fix: EmbeddedTargetOs on IBM i with Python 3.9

    For some context, Python 3.9 on IBM i returns "os400" for sys.platform
    instead of "aix". We used to build with Python 3.6 which returned "aix"
    as the platform

    When attempting to build Node.js with python 3.9 on IBM i we run into a
    build error.

    Ref: nodejs#48056
    Ref: nodejs#48056 (comment)

    I'm not quite sure where target_os is being passed down to the function ToEmbeddedTargetOs.
    It seems as though target_os is being generated from sys.platform or
    similar call from python as we started running into this issue after
    building with Python 3.9.

    This PR supersedes initial changes proposed in:
    https://chromium-review.googlesource.com/c/v8/v8/+/4259330

    This PR contains the minimal changes to successfully build Node.js (builds v8 as an internal dep)
    on IBM i with Python 3.9.

    Change-Id: I32d43197bce994a72a0d85091e91f80eeea4482d
    Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/4846413
    Commit-Queue: Jakob Linke <jgruber@chromium.org>
    Reviewed-by: Michael Achenbach <machenbach@chromium.org>
    Reviewed-by: Jakob Linke <jgruber@chromium.org>
    Cr-Commit-Position: refs/heads/main@{#89981}

Refs: v8/v8@8ec2651
PR-URL: nodejs#49639
Reviewed-By: Jiawen Geng <technicalcute@gmail.com>
Reviewed-By: Rafael Gonzaga <rafael.nunu@hotmail.com>
Reviewed-By: Antoine du Hamel <duhamelantoine1995@gmail.com>

common.gypi

@@ -36,7 +36,7 @@
 
     # Reset this number to 0 on major V8 upgrades.
     # Increment by one for each non-official patch applied to deps/v8.
-    'v8_embedder_string': '-node.11',
+    'v8_embedder_string': '-node.12',
 
     ##### V8 defaults for Node.js #####
 

deps/v8/src/snapshot/embedded/platform-embedded-file-writer-base.cc

@@ -130,7 +130,8 @@ EmbeddedTargetOs ToEmbeddedTargetOs(const char* s) {
   }
 
   std::string string(s);
-  if (string == "aix") {
+  // Python 3.9+ on IBM i returns os400 as sys.platform instead of aix
+  if (string == "aix" || string == "os400") {
     return EmbeddedTargetOs::kAIX;
   } else if (string == "chromeos") {
     return EmbeddedTargetOs::kChromeOS;