swift234

Extend the attributes machinery to enforce the "OnFoo" flags in Attr.def at sema time, and extend
them to cover all declaration types.

This ensures that we reject attributes on declkinds where they don't make sense.  I went so far
as to make the QoI decent when an attribute can only be applied to a single kind of declaration
to make sure the error message says "@IBAction is only valid on 'func' declarations" as well.

This resolves <rdar://problem/17681151> 'dynamic' accepted by the compiler where it shouldn't be




Swift SVN r19982