John Baldwin 3c2bc2bf26 Add a new atomic_fetchadd() primitive that atomically adds a value to a
variable and returns the previous value of the variable.

Tested on:	i386, alpha, sparc64, arm (cognet)
Reviewed by:	arch@
Submitted by:	cognet (arm)
MFC after:	1 week
2005-09-27 17:39:11 +00:00
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