swift234

Dynamically dispatch when delegating from a complete object initializer.

Inherited initializers are now functional: one can use an inherited
initializer to construct an object of a subclass type, and we properly
handle delegation to overridden complete object or subobject
initializers as appropriate. See the executable test.

This commit also contains various fixes for the IRGen side of vtable
emission and use. Proper IRGen tests still to come.

For now, we're still performing peer delegation from a subobject
initializer to another subobject initializer, hence the SILGen hack
for identifying when we're in a complete object vs. a subobject
initializer. We'll be banning delegation from subobject initializers,
so this hack---along with the peer_method instruction---will be going
away in the near future.



Swift SVN r14571