Really fix building android webview on mac.

Really fix building android webview on mac.

The refactoring in the final patchset landed as r269766 got the
condition backwards (the pre-refactoring version worked), so we were
accidentally excluding flag only on *target* builds, instead of host
builds as intended (the target compiler supports this flag). Fix it.

BUG=321833
R=primiano@chromium.org

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=272511

[Torne, 2014-05-23 09:35:53]

This is a fix for https://codereview.chromium.org/277983002/ which I screwed up
between PS1 and PS2. :)

[Primiano Tucci (use gerrit), 2014-05-23 09:48:17]

lgtm

[Torne, 2014-05-23 09:50:23]

The CQ bit was checked by torne@chromium.org

[commit-bot: I haz the power, 2014-05-23 09:52:33]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/torne@chromium.org/296273002/1

[commit-bot: I haz the power, 2014-05-23 13:30:46]

FYI, CQ is re-trying this CL (attempt #1).
Please consider checking whether the failures are real,
and report flakes to chrome-troopers@google.com.
The failing builders are:
  mac_chromium_rel on tryserver.chromium
(http://build.chromium.org/p/tryserver.chromium/builders/mac_chromium_rel/buil...)

[Torne, 2014-05-23 13:35:03]

Committed patchset #1 manually as r272511 (presubmit successful).