swift234

Make the definition of implicit default constructors lazy.

Tie the laziness into name lookup, so any attempt to look for the
constructors in a struct will ensure that the implicit default
constructor gets generated and added to the lookup set.

Laziness here is not about performance. Rather, it is a step toward
defining the implicit default constructor only when all instance
variables have implicit default constructors. Because Swift allows
struct definitions to come in any order, we need to wait until we've
done the first round of type-checking on declarations, then resolve
implicit default constructors as-needed, finalizing them all before
moving on to check function bodies.



Swift SVN r4888