Revert of Revert of clang: Suppress a -Wstring-conversion warnings in nspr.

Revert of Revert of clang: Suppress a -Wstring-conversion warnings in nspr. (patchset #1 id:1 of https://codereview.chromium.org/758303002/)

Reason for revert:
The CL only changed warning flags and had no effect other than disabling warnings. It doesn't affect code generation, linking, etc.

You can check that the NSS roll only brought in a single cl with a warning flag change here: https://chromium.googlesource.com/chromium/deps/nss/

Original issue's description:
> Revert of clang: Suppress a -Wstring-conversion warnings in nspr. (patchset #1 id:1 of https://codereview.chromium.org/754623004/)
>
> Reason for revert:
> Build failed:
> http://build.chromium.org/p/chromium.chrome/builders/Google%20Chrome%20Linux%20x64/builds/54166
> "ERROR: Shared library dependencies changed!"
>
> Unsure if this is the cause, but it looks like a clang roll a few weeks ago caused a similar error message (crbug.com/433065) so seeing if a revert fixes things :) sorry if this is the wrong CL!
>
> Original issue's description:
> > clang: Suppress a -Wstring-conversion warnings in nspr.
> >
> > Do the gn version directly, and roll the nss dep to pick up the gyp version.
> >
> > BUG=82385
> > R=hans@chromium.org
> >
> > Committed: https://chromium.googlesource.com/chromium/src/+/109b55f5bed033a46f10fd2f50093b82f03586f3
>
> TBR=hans@chromium.org,thakis@chromium.org
> NOTREECHECKS=true
> NOTRY=true
> BUG=82385
>
> Committed: https://crrev.com/60f77f2b85674ec3f681cce82b28b83c3beff596
> Cr-Commit-Position: refs/heads/master@{#305740}

TBR=hans@chromium.org,vrk@chromium.org
NOTREECHECKS=true
NOTRY=true
BUG=82385
Committed: https://crrev.com/24c0bd306a4ae854a9fc6ecf5db3bc810dacf055
Cr-Commit-Position: refs/heads/master@{#305748}

[Nico, 2014-11-26 00:58:49]

Created Revert of Revert of clang: Suppress a -Wstring-conversion warnings in
nspr.

[commit-bot: I haz the power, 2014-11-26 01:00:07]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/761683002/1

[commit-bot: I haz the power, 2014-11-26 01:01:15]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2014-11-26 01:02:12]

Patchset 1 (id:??) landed as
https://crrev.com/24c0bd306a4ae854a9fc6ecf5db3bc810dacf055
Cr-Commit-Position: refs/heads/master@{#305748}