update iOS build flags

update iOS build flags

This makes it match OS X build more closely.
The most important change is that CLANG_CXX_LIBRARY sets -stdlib=libc++
for both the compiler and the linker.

BUG=skia:

Committed: https://skia.googlesource.com/skia/+/1e5cbf2af7c1b818ba98e8a9da351aecfee320cb

[mtklein_C, 2015-11-16 22:06:35]

mtklein@chromium.org changed reviewers:
+ stephana@google.com

[stephana, 2015-11-16 22:37:22]

On 2015/11/16 22:06:35, mtklein_C wrote:

lgtm

[stephana, 2015-11-16 22:37:32]

The CQ bit was checked by stephana@google.com

[commit-bot: I haz the power, 2015-11-16 22:37:40]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1451913002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1451913002/1

[commit-bot: I haz the power, 2015-11-17 00:20:36]

Committed patchset #1 (id:1) as
https://skia.googlesource.com/skia/+/1e5cbf2af7c1b818ba98e8a9da351aecfee320cb