Update libc++/libc++abi build flags.

Update libc++/libc++abi build flags.

- Mysterious -pthread warning explained.
- Remove libc++abi link flags - it's a static library.
- Add some missing flags, sort list items.

BUG=none
R=jochen@chromium.org

Committed: a85661f97e83c620a8a1d0255829eb7a674e12cc

[earthdok, 2015-05-26 15:13:07]

earthdok@chromium.org changed reviewers:
+ jochen@chromium.org
- eisinger@chromium.org

[jochen (gone - plz use gerrit), 2015-05-26 15:51:30]

lgtm

[earthdok, 2015-05-26 15:51:53]

The CQ bit was checked by earthdok@chromium.org

[commit-bot: I haz the power, 2015-05-26 15:54:01]

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

[commit-bot: I haz the power, 2015-05-26 15:54:02]

Commit queue rejected this change because it did not recognize the base URL.
Please commit your change manually.

[earthdok, 2015-05-26 17:45:48]

On 2015/05/26 15:51:30, jochen wrote:
> lgtm

Updated: Added -fPIC, another missing flag.

I assume this can't be landed via CQ? Either way I don't think I have buildtools
commit access. Could you please land this for me?

[jochen (gone - plz use gerrit), 2015-05-27 07:37:40]

Committed patchset #2 (id:20001) manually as
a85661f97e83c620a8a1d0255829eb7a674e12cc (presubmit successful).

[earthdok, 2015-05-27 14:59:45]

On 2015/05/27 07:37:40, jochen wrote:
> Committed patchset #2 (id:20001) manually as
> a85661f97e83c620a8a1d0255829eb7a674e12cc (presubmit successful).

Thanks!