Atomic/SMP update, part 3.  (manual merge)

Update ARM atomic ops to use LDREX/STREX.  Stripped out #if 0 chunk.

Insert explicit memory barriers in pthread and semaphore code.

For bug 2721865.

Change-Id: I595cc8e5a8d1e4906b6641115e46208a7e9e755a
4 files changed