swift234

Rework default initialization of options to run much later, after all of the variables
have been type checked.  This allows us to reliably determine the type of the variable
and to know whether it actually needs default initialization or not.

This fixes:
<rdar://problem/16620121> Initializing constructor tries to initialize computed property overridden with willSet/didSet
which was because we were doing default initialization before computing override sets.

This does regress on one case, where our fiddly default init code isn't realizing that
a default initializer will be generated.  I fixme'd the case and filed:
<rdar://problem/16921173> implicit constructor synthesization runs too early

to track this.



Swift SVN r18094