atomic_min doesn't return old value for floats

[eaubanel]

I originally posted this on Discourse: https://discourse.julialang.org/t/atomic-min-for-floats/35880

Here is the MWM, copied from that post:

julia> E = Atomic{Float64}(10)
Atomic{Float64}(10.0)

julia> atomic_min!(E, 3.0)
3.0

julia> E
Atomic{Float64}(3.0)

atomic_min!(E, 3.0) should return 10.0 (i.e., the old value), not 3.0, as per the documentation. If I change the code to use Int64 then atomic_min() returns the old value (10).