[3.12] gh-109022: [Enum] require `names=()` to create empty enum type (GH-109048...

[3.12] gh-109022: [Enum] require `names=()` to create empty enum type (GH-109048) (#109122)

gh-109022: [Enum] require `names=()` to create empty enum type (GH-109048)

add guard so that ``Enum('bar')`` raises a TypeError instead of
creating a new enum class called `bar`.  To create the new but
empty class, use:

    huh = Enum('bar', names=())
(cherry picked from commit c74e440168fab9bf91346471087a394af13fa2db)

Co-authored-by: Ethan Furman <ethan@stoneleaf.us>