gn: make some warning flags match gyp more closely

gn: make some warning flags match gyp more closely

This fixes differences in -Wno-unused-function and
-Wno-unneeded-internal-declaration.

It also changes the diff'ing script to accept 

-Wendif-labels
-Wextra
-Wsign-compare

when in GN but not gyp, because they're more conservative. These
mostly happen when GN declares a lib chromium_code, but gyp doesn't.

Also, remove some defines from the dont_care, as I'm not sure that
we don't care yet.

And some minor tweaks to diff script output.

R=brettw@chromium.org
BUG=335824
Committed: https://crrev.com/e8d3adb185373b15d593855f623fb5e28ef7878c
Cr-Commit-Position: refs/heads/master@{#294229}

[brettw, 2014-09-10 00:13:34]

lgtm

[scottmg, 2014-09-10 18:00:26]

Patchset #6 (id:100001) has been deleted

[scottmg, 2014-09-10 18:20:31]

Patchset #6 (id:120001) has been deleted

[scottmg, 2014-09-10 18:50:44]

Patchset #5 (id:80001) has been deleted

[scottmg, 2014-09-10 18:50:52]

Patchset #5 (id:140001) has been deleted

[scottmg, 2014-09-10 18:50:55]

The CQ bit was checked by scottmg@chromium.org

[commit-bot: I haz the power, 2014-09-10 18:52:47]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/scottmg@chromium.org/555343002/160001

[commit-bot: I haz the power, 2014-09-10 19:20:19]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2014-09-10 19:20:20]

Try jobs failed on following builders:
  chromium_presubmit on tryserver.chromium.linux
(http://build.chromium.org/p/tryserver.chromium.linux/builders/chromium_presub...)
  linux_chromium_gn_rel on tryserver.chromium.linux
(http://build.chromium.org/p/tryserver.chromium.linux/builders/linux_chromium_...)

[scottmg, 2014-09-10 19:21:57]

scottmg@chromium.org changed reviewers:
+ thestig@chromium.org

[scottmg, 2014-09-10 19:22:29]

+thestig for breakpad/BUILD.gn -- made targets non-chromium_code which matches
gyp.

[scottmg, 2014-09-10 19:22:36]

The CQ bit was checked by scottmg@chromium.org

[commit-bot: I haz the power, 2014-09-10 19:23:23]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/scottmg@chromium.org/555343002/180001

[Lei Zhang, 2014-09-10 19:25:06]

lgtm

[commit-bot: I haz the power, 2014-09-10 19:37:20]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2014-09-10 19:37:21]

Try jobs failed on following builders:
  android_chromium_gn_compile_rel on tryserver.chromium.linux
(http://build.chromium.org/p/tryserver.chromium.linux/builders/android_chromiu...)

[scottmg, 2014-09-10 19:38:52]

The CQ bit was checked by scottmg@chromium.org

[commit-bot: I haz the power, 2014-09-10 19:39:51]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/scottmg@chromium.org/555343002/180001

[commit-bot: I haz the power, 2014-09-10 21:10:42]

Committed patchset #6 (id:180001) as 7cfe6ed8972c37b41518a26ddafcec2485f2760e

[commit-bot: I haz the power, 2014-09-10 21:25:31]

Patchset 6 (id:??) landed as
https://crrev.com/e8d3adb185373b15d593855f623fb5e28ef7878c
Cr-Commit-Position: refs/heads/master@{#294229}