[AllocBoxToStack] See through borrows.

Now that alloc_boxes whose lifetimes are lexical are emitted with
begin_borrow [lexical]/end_borrow, AllocBoxToStack needs to be able to
see through those new borrow scopes in order to continue stack promoting
the same boxes that it was able to before those lexical scopes were
emitted.

lib/SIL/IR/SILBuilder.cpp

@@ -285,6 +285,10 @@ SILBuilder::emitDestroyAddr(SILLocation Loc, SILValue Operand) {
     if (isa<DeallocStackInst>(Inst))
       continue;
 
+    // end_borrow insts also don't affect take-ability
+    if (isa<EndBorrowInst>(Inst))
+      continue;
+
     // An end_access of the same address may be able to be rewritten as a
     // [deinit] access.
     if (auto endAccess = dyn_cast<EndAccessInst>(Inst)) {