Allow anonymous check function

[jariji]

julia> @check function (x=Data.Floats{Float64}(nans=false))
           zero(x) ≤ abs(x)
       end
ERROR: LoadError: ArgumentError: Given expression is not a function head expression!

I want to use syntax like this sometimes. I know it's good practice to give a name and helpful for when it shows Context but sometimes I'm just experimenting and don't want to think up a name.