Teach Ninja generator about 'AR' in 'make_global_settings'

Teach Ninja generator about 'AR' in 'make_global_settings'

With this CL, 'AR' in 'make_global_settings' can be recognized by Ninja generator, like Make generator. This makes it easier for you to share the code among host/NaCl/NDK/Emscripten build targets.

Note that 'AR.host' is not yet supported with this CL.

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

Committed: https://code.google.com/p/gyp/source/detail?r=1935

[yukawa, 2014-06-09 17:58:38]

Hi Scott, Torne,
Can you take a look?

I hope the diff of gyptest-make_global_settings_ar.py describes well about the
change.

[scottmg, 2014-06-11 22:54:49]

lgtm

[yukawa, 2014-06-12 17:35:53]

Committed patchset #2 manually as r1935 (presubmit successful).