Remove the intent to turn on Wextra for gcc (except MacOS)

Remove the intent to turn on Wextra for gcc (except MacOS).

We use clang with Wextra which seems to be more reliable and report less false positives. We no longer have an intent to turn on Wextra for gcc on posix-like systems any more (except MacOS).

Committed: https://crrev.com/2ca5097c4db8905beba3c37a47f40b21b97877a0
Cr-Commit-Position: refs/heads/master@{#322101}

[lgombos, 2015-03-24 20:50:14]

l.gombos@samsung.com changed reviewers:
+ thakis@chromium.org

[lgombos, 2015-03-24 20:50:14]

Nico, would you mind rubber stamping this this CL again ?

Commit queue is not picking up the CL that you reviewed yesterday
(https://codereview.chromium.org/61643017) probably because it still points to
an SVN base url and even though I have git locally I am not able to migrate that
CL into a git checkout - so maybe just easier to redo it.

[Nico, 2015-03-24 21:11:31]

lgtm

[lgombos, 2015-03-24 21:29:19]

The CQ bit was checked by l.gombos@samsung.com

[commit-bot: I haz the power, 2015-03-24 21:29:39]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1029953003/1

[commit-bot: I haz the power, 2015-03-25 00:11:54]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-03-25 00:12:51]

Patchset 1 (id:??) landed as
https://crrev.com/2ca5097c4db8905beba3c37a47f40b21b97877a0
Cr-Commit-Position: refs/heads/master@{#322101}