Add unittest for 'AR' in 'make_global_settings'

Add unittest for 'AR' in 'make_global_settings'

Currently sharing the code among host/NaCl/NDK/Emscripten on top of Ninja+gyp isn't so easy as it should be because not all items in 'make_global_settings' are recognized by Ninja generator (gyp:434).

On the other hand, the current test coverage of 'make_global_settings' isn't so good. Thus this CL describes the current behavior with some unittests before making Ninja generator aware of 'AR' in 'make_global_settings' like Make generator.

BUG=gyp:434
TEST=unittest
R=scottmg@chromium.org

Committed: https://code.google.com/p/gyp/source/detail?r=1931

[yukawa, 2014-06-08 18:12:38]

Hey Scott,
Can you take a look at this CL?

Though this CL never changes existing behavior, my final goal is to make 'AR' in
'make_global_settings' recognized by Ninja generator (in some subsequent CLs). 
Please let me know if any concerns about this plan itself.

Thanks!

[scottmg, 2014-06-09 16:02:37]

This lgtm, but adding Torne and Ami who have expressed more interest/know more
about .host compiles for the overall question.

[Torne, 2014-06-09 16:06:38]

As long as this is consistent with the other settings this should be fine.

[yukawa, 2014-06-09 16:37:50]

On 2014/06/09 16:06:38, Torne wrote:
> As long as this is consistent with the other settings this should be fine.

Thanks.  I believe my subsequent CLs improve the consistency between Ninja
generator and Make generator, rather than introducing any breaking changes. 
Anyway, I'll make sure it by asking you guys to review subsequent CLs.  Please
let me know at that time if you find something.

Ami, do you have any concerns?

[Ami GONE FROM CHROMIUM, 2014-06-09 16:44:03]

I think the stated goal is a good one.  Leaving actual review to others.

[yukawa, 2014-06-09 17:11:29]

Committed patchset #1 manually as r1931 (presubmit successful).