ART: Make LOCAL_CLANG architecture dependent for the target

Be selective for which target we compile with Clang. Currently we
only want to compile with Clang for ARM64, which means we need to
be careful about ARM, which is the second architecture for that.

Bug: 15014252
Change-Id: I239591f65eab537deac39a25bd20530dce5c4786
7 files changed