LLVM FP atomic min/max variants alignment

Hello,

Gonzalo is working on adding the new FP atomic min/max variants to 
libc++.  He'd like to ensure that whatever builtins he adds will not 
conflict with anything we decide to do in the future.

I'll let him explain the details and list the points he'd like to align 
on.  I'm sending this email to make introductions and to ease finding 
the addresses to Cc.

I believe the only thing to be concerned about are the names (because 
IIUC clang doesn't specify the FP environment semantics) but am Cc'ing 
in Joseph Myers for visibility in case I'm wrong about that.

Cheers,
Matthew