Add support for compiling Android from MacOS ARM64 host

A set of changes that modifies the build files (gni, gn, py, and DEPS) in order to extend support to MacOS. The need for patching these was mostly because the entire build logic assumes that the host OS is "Linux" ending up with the wrong dependencies.
Most of the changes include comments to clarify their purpose.

V8 CL: https://crrev.com/c/5957090

Bug: 41173821
Change-Id: I48d9ed7202ab87c24c6f943c5ac00720c53bcf00
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5947626
Reviewed-by: Nico Weber <[email protected]>
Reviewed-by: Andrew Grieve <[email protected]>
Commit-Queue: Andrew Grieve <[email protected]>
Cr-Commit-Position: refs/heads/main@{#1373956}


CrOS-Libchrome-Original-Commit: 805cfbc3d7abb96776282ba83c4d5ae6483d9f40

Author: Simone Arpe

build/android/gyp/util/parallel.py

@@ -26,6 +26,10 @@
 _fork_params = None
 _fork_kwargs = None
 
+# Ensure fork is used on MacOS for multiprocessing compatibility.
+# Starting from Python 3.8, the "spawn" method is the default on MacOS.
+# On Linux hosts this line will be a no-op.
+multiprocessing.set_start_method('fork')
 
 class _ImmediateResult:
   def __init__(self, value):

build/android/gyp/util/server_utils.py

@@ -7,6 +7,7 @@
 import os
 import pathlib
 import socket
+import platform
 
 # Use a unix abstract domain socket:
 # https://man7.org/linux/man-pages/man7/unix.7.html#:~:text=abstract:
@@ -17,6 +18,10 @@
 def MaybeRunCommand(name, argv, stamp_file, force):
   """Returns True if the command was successfully sent to the build server."""
 
+  if platform.system() == "Darwin":
+    # Build server does not support Mac.
+    return False
+
   # When the build server runs a command, it sets this environment variable.
   # This prevents infinite recursion where the script sends a request to the
   # build server, then the build server runs the script, and then the script