GN: Simplify config by unconditionalising a flag that nacl-clang recognises

GN: Simplify config by unconditionalising a flag that nacl-clang recognises

Use of the flag "-Wno-inconsistent-missing-override" no longer needs
to be conditionalised.

This is also a step towards getting Skia to build with the (P)NaCl
toolchains, because Skia currently needs to be compiled with this
warning disabled.

BUG=https://github.com/domokit/mojo/issues/431
TEST=build

Committed: https://crrev.com/1ff21d98978803710edc806ca3eda3bb79c5107a
Cr-Commit-Position: refs/heads/master@{#349511}

[Mark Seaborn, 2015-09-17 19:48:16]

mseaborn@chromium.org changed reviewers:
+ dpranke@chromium.org

[Mark Seaborn, 2015-09-17 19:48:17]

This is to upstream a Mojo-side change,
https://codereview.chromium.org/1349933003/.

[Dirk Pranke, 2015-09-17 20:08:43]

lgtm

[Mark Seaborn, 2015-09-17 20:42:47]

The CQ bit was checked by mseaborn@chromium.org

[commit-bot: I haz the power, 2015-09-17 20:44:02]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1351683004/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1351683004/1

[commit-bot: I haz the power, 2015-09-17 22:10:52]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-09-17 22:11:32]

Patchset 1 (id:??) landed as
https://crrev.com/1ff21d98978803710edc806ca3eda3bb79c5107a
Cr-Commit-Position: refs/heads/master@{#349511}