Ensure that _GNU_SOURCE is defined early enough

Ensure that _GNU_SOURCE is defined early enough

This style cleanup broke some versions of glibc that include fcntl.h from
another header before it is explicitly included:
https://codereview.chromium.org/236083002/

We need _GNU_SOURCE defined before the first time fcntl.h is included since
we use the linux-specific O_DIRECTORY extension.

Thanks to johan_e@opera.com for helping track this down.

NOTRY=true

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=269419

[Mostyn Bramley-Moore, 2014-05-06 09:33:56]

@jln, rsesek: PTAL at this fixup.

[jln (very slow on Chromium), 2014-05-08 00:50:44]

Thanks, lgtm!

[Mostyn Bramley-Moore, 2014-05-08 07:11:25]

The CQ bit was checked by mostynb@opera.com

[commit-bot: I haz the power, 2014-05-08 07:13:29]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/mostynb@opera.com/266913019/20001

[commit-bot: I haz the power, 2014-05-08 20:27:20]

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:
  win_chromium_rel on tryserver.chromium
(http://build.chromium.org/p/tryserver.chromium/builders/win_chromium_rel/buil...)

[Mostyn Bramley-Moore, 2014-05-08 20:49:44]

The CQ bit was unchecked by mostynb@opera.com

[Mostyn Bramley-Moore, 2014-05-08 20:49:44]

The CQ bit was checked by mostynb@opera.com

[commit-bot: I haz the power, 2014-05-08 20:52:32]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/mostynb@opera.com/266913019/20001

[Mostyn Bramley-Moore, 2014-05-08 22:31:51]

The CQ bit was unchecked by mostynb@opera.com

[Mostyn Bramley-Moore, 2014-05-08 22:33:42]

This CL only touches *_linux.cc files, and is being blocked in the CQ due to
win_chromium_rel flakiness (all other try jobs succeeded), so requeuing with
NOTRY=true...

[Mostyn Bramley-Moore, 2014-05-08 22:33:47]

The CQ bit was checked by mostynb@opera.com

[commit-bot: I haz the power, 2014-05-08 22:39:20]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/mostynb@opera.com/266913019/20001

[commit-bot: I haz the power, 2014-05-09 21:41:05]

Change committed as 269419