[PATCH] CFE Knob for: Add a thread-model knob for lowering atomics on baremetal & single threaded systems

[Jonathan Roelofs]

ping

@t.p.northover do you have a better suggestion on the thread model's name? We could try to match gcc here, as I've half-heartedly done (I didn't add the bits that make it print out "win32" on windows), or we could do something else.

http://reviews.llvm.org/D4985