The following revision refers to this bug:
  https://chromium.googlesource.com/chromiumos/overlays/chromiumos-overlay/+/de62c8a6784ac3b0835a8ce6d78cfa363e4bf135

commit de62c8a6784ac3b0835a8ce6d78cfa363e4bf135
Author: Chih-Yu Huang <akahuang@google.com>
Date: Fri Jan 18 17:04:17 2019

arc-build.eclass: Add argument "stdlib=libc++" in CXX

We plan to build ARC++ code at ChromiumOS repo.
In platform2 GN toolchain, we don't pass CXXFLAGS to the linker.
"-stdlib=libc++" argument is missing there. Therefore we add this
argument at the CXX variable directly.

BUG=b:118848258
BUG=chromium:922335
TEST=Run `emerge-eve hammerd` and no error
TEST=Run `emerge-eve arc-codec-test` with following CL

Change-Id: I2abaa56e71407ae44b56f29dbc56cd6bea97246b
Reviewed-on: https://chromium-review.googlesource.com/1404780
Commit-Ready: Chih-Yu Huang <akahuang@chromium.org>
Tested-by: Chih-Yu Huang <akahuang@chromium.org>
Reviewed-by: Chih-Yu Huang <akahuang@chromium.org>

[modify] https://crrev.com/de62c8a6784ac3b0835a8ce6d78cfa363e4bf135/eclass/arc-build.eclass