Fix to build sdch target under clang.

Fix to build sdch target under clang and gcc 4.8 when in c++11 mode.

This ports the gyp's changes from r258918 (
https://codereview.chromium.org/205963004/)

To test:

$ gn gen out/Release_gn --args='is_debug=false is_clang=true'
$ ninja -C out/Release_gn sdch

BUG=367597, 324299
TEST=see above
R=brettw@chromium.org
TBR=brettw

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=267039

[Nico, 2014-04-28 03:24:54]

(From the Cl description of the Cl you're linking to: "This is also needed for
c++11 mode in gcc 4.8, not just clang.")

[tfarina, 2014-04-28 04:41:37]

On 2014/04/28 03:24:54, Nico wrote:
> (From the Cl description of the Cl you're linking to: "This is also needed for
> c++11 mode in gcc 4.8, not just clang.")

Thanks. I added that information to the CL description.

[Mostyn Bramley-Moore, 2014-04-28 08:39:43]

Non-owner lgtm.

Tested with gcc 4.8.1 and it seems to work, however I need to build with
-Wno-unused-local-typedefs.  Filed http://crbug.com/367657 to fix that.

[tfarina, 2014-04-30 01:44:44]

Brett, I'm committing this.

Feel free to yell at me if you want me to revert this or to fix it in another
way.

[tfarina, 2014-04-30 01:49:39]

Committed patchset #1 manually as r267039 (presubmit successful).