This is part of a series of commits to remove reference forwarding for

some of the ARC entry points. rdar://22724641. After this commit,
swift_retain_noresult will be completely replaced by swift_retain.
LLVMARCOpts pass is modified NOT to rewrite swift_retain to
swift_retain_noresult which forward no reference.

Swift SVN r32082

stdlib/public/runtime/Casting.cpp

@@ -941,7 +941,7 @@ static bool _dynamicCastToExistential(OpaqueValue *dest,
     auto object = *(reinterpret_cast<HeapObject**>(srcDynamicValue));
     destExistential->Value = object;
     if (!canTake || !(flags & DynamicCastFlags::TakeOnSuccess)) {
-      swift_retain_noresult(object);
+      swift_retain(object);
     }
     maybeDeallocateSourceAfterSuccess();
     return true;