Set host_arch to ia32 on machines with a 32bit userland but a 64bit kernel.

Set host_arch to ia32 on machines with a 32bit userland but a 64bit kernel.

I don't know if there are any v8 bots with that configuration, but it seems
like a good idea to have v8 be consistent with chromium and nacl here, so that
this works fine if such a bot is ever set up.

This is similar to https://codereview.chromium.org/342493002/ , but with a
detect_v8_host_arch.py script that handles the additional machine types that
standalone.gypi used to handle.

Originally reviewed at https://codereview.chromium.org/346643002/

BUG=368384
LOG=Y
R=jochen@chromium.org

Committed: https://code.google.com/p/v8/source/detail?r=21956

[jochen (gone - plz use gerrit), 2014-06-24 07:12:23]

On 2014/06/24 at 04:39:57, thakis wrote:
> 

lgtm

I also fixed Makefile for you

[jochen (gone - plz use gerrit), 2014-06-24 07:13:41]

Committed patchset #3 manually as r21956 (presubmit successful).