The comment in https://code.google.com/p/chromium/codesearch#chromium/src/build/config/BUILDCONFIG.gn&q=is_linux%20file:%5Esrc/build/&sq=package:chromium&type=cs&l=252 suggests that the OS check supports these OS'es. It is automatically set in host_os, the rest is derived. I didn't find documentation about the exact string values that will end up in host_os and if they are the same as in gyp.

The code location in gn suggests that the above named OSes are not supported yet: https://code.google.com/p/chromium/codesearch#chromium/src/tools/gn/args.cc&sq=package:chromium&type=cs&l=217&rcl=1464664581

As suggested by laforge@ and a conversation w/ the monorail folks, I'm going to try tracking V8 GN-Migration related issues by *just* using the Proj-GN-Migration-V8 label, and not using blocking/rollup bugs, so that we can use blocking for just tasks that truly need to be completed before other tasks can make progress.

This issue has been Available for over a year. If it's no longer important or seems unlikely to be fixed, please consider closing it out. If it is important, please re-triage the issue.

Sorry for the inconvenience if the bug really should have been left as Available. If you change it back, also remove the "Hotlist-Recharge-Cold" label.

For more details visit https://www.chromium.org/issue-tracking/autotriage - Your friendly Sheriffbot

AIX is done by  issue 706728 

The following revision refers to this bug:
  https://chromium.googlesource.com/v8/v8.git/+/13d67667cc5ffa52457e654a0a44c89aefbca6f7

commit 13d67667cc5ffa52457e654a0a44c89aefbca6f7
Author: Vasili Skurydzin <vasili.skurydzin@ibm.com>
Date: Thu Feb 08 17:51:44 2018

Fixes to V8 GN build process on AIX

Change to v8/BUILD.gn regarding GN build of V8. Excluding platform-posix-time.h
and platform-posix-time.cc from the sources list on AIX os. The changes affect
AIX only.

Bug: chromium:616029
Change-Id: I5e5d46aa4c62f70544ff593294e459c607a03c67
Reviewed-on: https://chromium-review.googlesource.com/897124
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#51183}
[modify] https://crrev.com/13d67667cc5ffa52457e654a0a44c89aefbca6f7/BUILD.gn