Enable clang/llvm for arm64 and mips targets.

Only arm64 and mips targets use c11 atomic functions now,
depending on JEMALLOC_C11ATOMICS in include/jemalloc/internal/atomic.h.

BUG: 21119263
Change-Id: I8f60207e3e677d57a0b9b9d73224fc985057121d
3 files changed