Subzero: Change llvm::OwningPtr to C++11's std::unique_ptr.

While I'm at it, normalize the #include order:

1. C++ library headers
2. LLVM headers
3. Subzero headers

A blank line between each group.  Each group sorted alphabetically, case-insensitive.

BUG= https://code.google.com/p/nativeclient/issues/detail?id=3930
R=jfb@chromium.org, jvoung@chromium.org

Review URL: https://codereview.chromium.org/622443002
diff --git a/src/IceDefs.h b/src/IceDefs.h
index 68f30c7..2555b20 100644
--- a/src/IceDefs.h
+++ b/src/IceDefs.h
@@ -16,9 +16,8 @@
 #ifndef SUBZERO_SRC_ICEDEFS_H
 #define SUBZERO_SRC_ICEDEFS_H
 
-#include <stdint.h> // TODO: <cstdint> with C++11
-
 #include <cassert>
+#include <cstdint>
 #include <cstdio>     // snprintf
 #include <functional> // std::less
 #include <limits>