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/IceTargetLowering.h b/src/IceTargetLowering.h
index 37e14df..1995124 100644
--- a/src/IceTargetLowering.h
+++ b/src/IceTargetLowering.h
@@ -19,9 +19,8 @@
 #define SUBZERO_SRC_ICETARGETLOWERING_H
 
 #include "IceDefs.h"
-#include "IceTypes.h"
-
 #include "IceInst.h" // for the names of the Inst subtypes
+#include "IceTypes.h"
 
 namespace Ice {