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_icmp.h b/crosstest/test_icmp.h
index 52a9f22..8a264d0 100644
--- a/crosstest/test_icmp.h
+++ b/crosstest/test_icmp.h
@@ -28,7 +28,7 @@
 #undef X
 
 #define X(cmp, op)                                                             \
-  bool icmp##cmp(int8_t a, int8_t b);                                          \
+  bool icmp##cmp(myint8_t a, myint8_t b);                                      \
   bool icmp##cmp(int16_t a, int16_t b);                                        \
   bool icmp##cmp(int32_t a, int32_t b);                                        \
   bool icmp##cmp(int64_t a, int64_t b);                                        \