swift234

Sema: Reject @objc functions with generic parameters

We currently complain about this type of thing:

class C<T> {
  @objc func foo() -> [T]
}

However this is also not supported, but crashes in IRGen:

class C {
  @objc func foo<T>() -> [T]
}

Also re-word a @nonobjc diagnostic and clean up some code for @objc and
@nonobjc.

Fixes <rdar://problem/19600602> and <rdar://problem/20886887>.

Swift SVN r29117