deps: cherry-pick a51f429 from V8 upstream

Original commit message:

  Use gn from PATH on aix

  Change-Id: I853f7899dbba9112ba1ca2ce78e2838b5a09c975
  Reviewed-on: https://chromium-review.googlesource.com/1168087
  Commit-Queue: John Barboza <jbarboza@ca.ibm.com>
  Reviewed-by: Michael Achenbach <machenbach@chromium.org>
  Cr-Commit-Position: refs/heads/master@{#55028}

PR-URL: #23695
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>
Reviewed-By: Refael Ackermann <refack@gmail.com>
Reviewed-By: Yang Guo <yangguo@chromium.org>
Reviewed-By: Ujjwal Sharma <usharma1998@gmail.com>

common.gypi

@@ -33,7 +33,7 @@
 
     # 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.40',
+    'v8_embedder_string': '-node.41',
 
     # Enable disassembler for `--print-code` v8 options
     'v8_enable_disassembler': 1,

deps/v8/tools/mb/mb.py

@@ -832,14 +832,12 @@ def GNCmd(self, subcommand, path, *args):
       subdir, exe = 'linux64', 'gn'
     elif self.platform == 'darwin':
       subdir, exe = 'mac', 'gn'
-    elif self.platform == 'aix6':
-      subdir, exe = 'aix', 'gn'
     else:
       subdir, exe = 'win', 'gn.exe'
 
     arch = platform.machine()
-    if (self.platform == 'linux2' and
-       (arch.startswith('s390') or arch.startswith('ppc'))):
+    if (arch.startswith('s390') or arch.startswith('ppc') or
+        self.platform.startswith('aix')):
       # use gn in PATH
       gn_path = 'gn'
     else: