Subzero: The cross tests should use the actual Subzero runtime.

runtime/szrt.cpp

+//===- subzero/runtime/szrt.cpp - Subzero runtime source ------------------===//
+//
+//                        The Subzero Code Generator
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file is a C++ wrapper to szrt.c since clang++ complains about
+// .c files.
+//
+//===----------------------------------------------------------------------===//
+
+extern "C" {
+#include "szrt.c"
+}