Now we have enabled arm64 clang.
This change remvoed arm64 clang build warning and cleaned the
arm64 unknow c flags.
Change-Id: Ia583a78c6d364e603ff09df423aa34a6e03d0b9b
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
Chih-Hung Hsieh