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

runtime/szrt.cpp

Index: runtime/szrt.cpp
diff --git a/runtime/szrt.cpp b/runtime/szrt.cpp
new file mode 100644
index 0000000000000000000000000000000000000000..62afa06da9f5c3847b309784f92af4cdf88c5443
--- /dev/null
+++ b/runtime/szrt.cpp
@@ -0,0 +1,17 @@
+//===- 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"
+}