swift234

Allow to one to define zero-parameter initializers with Objective-C names longer than "init".

There are a handful of Objective-C initializers with names like
"initForMemory" that take no parameters. The Clang importer has long
been importing them with a single parameter of type (), e.g.,

  init(forMemory: ())

At some point, our @objc checking got stricter and started rejecting
parameters of type (), making it impossible to define such an
initializer in Swift. Codify this case in @objc checking, fixing
rdar://problem/19973250.

Swift SVN r25611