[objc] If an interface has no initializer marked as designated and introduces...

[objc] If an interface has no initializer marked as designated and introduces at least one new initializer,
don't assume that it inherits the designated initializers from the super class.

If the assumption was wrong because a new initializer was a designated one that was not marked as such,
we will emit misleading warnings for subclasses of the interface.

llvm-svn: 196476