Prototype libatomic

[Andrew MacLeod]

One of the things I want to make sure is that the library can be easily 
extended in a generic way (ie not target dependant) as needs change.  
Ie, initiually we are simply guaranteeing atomic operations and fall 
back to a lock.

I expect in the not too distant future other sorts of guarantees may be 
desired, such as various forms of forward progress guarantees to replace 
the spin locks, and It'd be nice to have a TM version of the library as 
well, so when hardware is available we can make good use of it.

That sort of thing :-)

Perhaps those can fall into the config directory as well?  ie  
config/TM  or config/forwardprogress?    or would that fall in place 
better as new files the libatomic directory (or new subdirectories) and 
using any new info enabled from the various config/target directories....

Andrew