Subzero: Fix and clean up some cross tests.

crosstest/test_cast.h

+//===- subzero/crosstest/test_cast.h - Test prototypes ----------*- C++ -*-===//
+//
+//                        The Subzero Code Generator
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file declares the function prototypes used for crosstesting cast
+// operations.
+//
+//===----------------------------------------------------------------------===//
+
+// The driver and the test program may be compiled by different
+// versions of clang, with different standard libraries that have
+// different definitions of int8_t.  Specifically, int8_t may be
+// typedef'd as either 'char' or 'signed char', which mangle to
+// different strings.  Avoid int8_t and use an explicit myint8_t.
+typedef signed char myint8_t;
+
 template <typename FromType, typename ToType> ToType cast(FromType a);
 template <typename FromType, typename ToType> ToType castBits(FromType a);