Base: slight simplification in int.jl

[nsajko]

Use ~, zero and shifts to simplify the definitions of typemin and typemax.

[vtjnash]

This seems likely unnecessarily harder for the compiler to constant evaluate, and incorrectly switches the position / ordering of Union and Type

[nsajko]

Why is "harder for the compiler to constant evaluate" a problem? Naively, I'd think that would only be a problem the first time Julia compiles the relevant method?

incorrectly switches the position / ordering of Union and Type

What does this mean? Does it refer to the fact that, with this commit, methods like typemin(::Union{Int8,Int16}) exist, but result in a MethodError when called? If that's an issue, I think I could fix it using traits.

[vtjnash]

Union{map(t -> Type{t}, BitSigned_types)...} is also valid for that, but still doesn't seem like a simplification

[nsajko]

Why is typemin accepting calls like typemin(Union{Int8,Int16}) a problem in the first place? Seems like where {T<:Union{...}} is a common pattern otherwise in Julia.

I'm asking because I'm interested in somewhat similar but more significant changes elsewhere in Base.