Swift backend doesn't support single entry enums

[chiroptical]

data X = X

mobileGenWith (defaultOptions {dataRawValue = Just Str}) ''X

should be able to produce

enum X {
  case x
}

Currently we have an error specific to swift here

moat/src/Moat.hs

Lines 525 to 532 in 2eda1d2

	SingleConNonRecord (nameStr -> n) ->
	n
	++ ": Cannot get moat with single-constructor "
	++ "non-record types. This is due to a "
	++ "restriction of Swift that prohibits structs "
	++ "from not having named fields. Try turning "
	++ n
	++ " into a record!"

but apparently this works fine.