Move to a single clang unknown flags list

Soong is using a single list of unknown clang flags for all
architectures, instead of the per-architecture list here. Collapse this
down to a single list as well so that it can be verified against the
Soong list, and eventually replaced by the Soong version.

Change-Id: If43cd892105da5155907c05965a74b835920a369
16 files changed