Atomic/SMP update. [manual merge to dalvik-dev]

Added atomic-inline.h.  Added a platform-specific memory barrier call
there.

Added android_atomic_acquire_cmpxchg() and android_atomic_release_store().
Not tested on Mac OS X or SH.

Added memory barrier calls to linux-x86 atomics.  Mac OS X has barrier
functions already.  sh isn't really SMP-ready.  linux-arm needs work
(to be done in a separate change).

Updated the makefile to make the SMP state visible to the code here.
Note that host binaries are NOT built with SMP enabled; while our hosts
are very likely SMP, it's not worth figuring out e.g. whether it's okay
to use the SSE2 mfence instruction or have to use something else.  We
haven't had barriers enabled in host tools before, so there's probably
no need to stat now.

Removed quasiatomic 64-bit calls (now part of Dalvik).

Change-Id: I42ae05f5db2cc9a5b64ad87f15481e2838371f1d