Subzero: Fix and clean up some cross tests.

1. It turns out that the crosstest scripts mix different versions of
clang - build_pnacl_ir.py uses pnacl-clang from the NaCl SDK for the
tests, while crosstest.py uses clang/clang++ from LLVM_BIN_PATH for
the driver.  The SDK has been updated to use a different version of
the standard library, and now there is a mismatch as to whether int8_t
is typedef'd to 'char' or 'signed char', leading to name mangling
mismatches.  (char, signed char, and unsigned char are distinct
types.)  We deal with this by using myint8_t which is explicitly
defined as signed char.

2. Some ugly function pointer casting in test_arith_main.cpp is fixed/removed.

3. std::endl is replaced with "\n".

4. License text is added to tests that were touched by the above items.

BUG= none
R=wala@chromium.org

Review URL: https://codereview.chromium.org/435353002
diff --git a/crosstest/test_vector_ops.def b/crosstest/test_vector_ops.def
index 422ed54..3396d43 100644
--- a/crosstest/test_vector_ops.def
+++ b/crosstest/test_vector_ops.def
@@ -1,3 +1,17 @@
+//===- subzero/crosstest/test_vector_ops.def - test macros ----*- C++ -*---===//
+//
+//                        The Subzero Code Generator
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file defines macros for crosstesting the insertelement and
+// extractelement instruction.
+//
+//===----------------------------------------------------------------------===//
+
 #ifndef TEST_VECTOR_OPS_DEF
 
 #define VECTOR_TYPE_TABLE                 \