Add fetch_and, fetch_or, fetch_nand, fetch_xor to AtomicInt, AtomicUint

[brson]

I don't see any reason these shouldn't exist.

[alexcrichton]

cc #8151 and #10154

It appears that we removed these originally because they were lowered to intrinsic calls on arm. Now that we're linking to compiler-rt, though (and passing v7 by default on arm), this is probably fine.