alloc_stack needs to return two values like alloc_box.

The current implementation of dealloc_stack in IR-gen is a
no-op, but that's very much wrong for types with non-trivial
local allocation requirements, e.g. archetypes.  So we need
to be able to do non-trivial code here.  However, that means
modeling both the buffer pointer and the allocated address
in SIL.

To make this more type-safe, introduce a SIL-specific
'[local_storage] T' type that represents the required
allocation for locally storing a T.  alloc_stack now returns
one of those in additon to a *T, and dealloc_stack expects
the former.

IR-gen still implements dealloc_stack as a no-op, but
that's now easy to fix.

Swift SVN r6937

lib/Serialization/ModuleFile.cpp

@@ -1671,6 +1671,14 @@ Type ModuleFile::getType(TypeID TID) {
     break;
   }
 
+  case decls_block::LOCAL_STORAGE_TYPE: {
+    TypeID valueTypeID;
+    decls_block::LocalStorageTypeLayout::readRecord(scratch, valueTypeID);
+
+    typeOrOffset = LocalStorageType::get(getType(valueTypeID), ctx);
+    break;
+  }
+
   case decls_block::REFERENCE_STORAGE_TYPE: {
     uint8_t rawOwnership;
     TypeID referentTypeID;