Add -Wno-invalid-offsetof to Mac and iOS builds too.

Add -Wno-invalid-offsetof to Mac and iOS builds too.

We use this on Linux already, but for whatever reason wasn't a problem on iOS
until using it in SkPaint.  Mac 10.7 and 10.8 are showing this warning too,
but seems -Werror is not enabled.

CQ_EXTRA_TRYBOTS=tryserver.skia:Build-Mac10.7-Clang-Arm7-Release-iOS-Trybot

BUG=skia:

Committed: https://skia.googlesource.com/skia/+/38ba4e0588bc01dedbe8b14cf990a6f4ffe92fc7

[mtklein, 2014-10-07 16:39:45]

mtklein@google.com changed reviewers:
+ mtklein@google.com

[mtklein, 2014-10-07 16:39:45]

The CQ bit was checked by mtklein@google.com

[mtklein, 2014-10-07 16:39:46]

lgtm

[commit-bot: I haz the power, 2014-10-07 16:40:31]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/637593002/1

[commit-bot: I haz the power, 2014-10-07 16:54:22]

Committed patchset #1 (id:1) as 38ba4e0588bc01dedbe8b14cf990a6f4ffe92fc7

[tfarina, 2014-10-07 20:05:52]

tfarina@chromium.org changed reviewers:
+ tfarina@chromium.org

[tfarina, 2014-10-07 20:05:53]

lgtm

https://codereview.chromium.org/637593002/diff/1/gyp/common_conditions.gypi
File gyp/common_conditions.gypi (right):

https://codereview.chromium.org/637593002/diff/1/gyp/common_conditions.gypi#n...
gyp/common_conditions.gypi:512: '-Wno-invalid-offsetof',
looks fine, below too.