fix <rdar://problem/20608881> DI miscompiles this testcase into a memory leak

When emiting logic for conditional destruction of a variable, we weren't considering
a delegated init as a store to the variable that needed to be tracked.  This caused us
to miscompile situations like this testcase where the self.init was conditional:

struct X {
  var c : C
  init() { c = C()}
  init?(a : Bool) {
    if a { self.init() }
    return nil
  }
}

This was exposed by other work, but needs to be fixed in any case.



Swift SVN r27471

lib/SILPasses/DefiniteInitialization.cpp

@@ -1493,6 +1493,7 @@ SILValue LifetimeChecker::handleConditionalInitAssign() {
       // The dynamically unknown case is the interesting one, handle it below.
       break;
 
+    case DIUseKind::SelfInit:
     case DIUseKind::Initialization:
       // If this is an initialization of only trivial elements, then we don't
       // need to update the bitvector.