Update toolchain_args to new GN format.
Update toolchain_args to new GN format.

TBR=bradnelson

Review-Url: https://codereview.chromium.org/2304683002

sbc100/native_client,sbc100/native_client,sbc100/native_client,sbc100/native_client,sbc100/native_client,sbc100/native_client