This lays the groundwork for making builds hermetic on Darwin as well.
That will be fixed in a future patch.
bug 13435344
Change-Id: Iae82d0b9efad0598d682ff5fd4daa737aa607866
1. Following the setup of gcc in build/core/combo/,
we added the [HOST|TARGET]_<arch>.mk clang config files,
and load only the configs needed by the current product.
2. Added support for the 2nd arch.
Change-Id: I2a383418a9688a050b39492f8e489d40eeeb5f2d