Change the canonical way to include the C macros.h to <mojo/macros.h>.

mojo/public/c/include/mojo/macros.h

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#ifndef MOJO_PUBLIC_C_SYSTEM_MACROS_H_
-#define MOJO_PUBLIC_C_SYSTEM_MACROS_H_
+#ifndef MOJO_PUBLIC_C_INCLUDE_MOJO_MACROS_H_
+#define MOJO_PUBLIC_C_INCLUDE_MOJO_MACROS_H_
 
 #include <stddef.h>
 
 // Annotate a variable indicating it's okay if it's unused.
 // Use like:
 //   int x = ...;
 //   MOJO_ALLOW_UNUSED_LOCAL(x);
 #define MOJO_ALLOW_UNUSED_LOCAL(x) false ? (void)x : (void)0
 
 // Annotate a function indicating that the caller must examine the return value.
@@ skipping 62 matching lines @@
 // which is to non-const, then all the pointer parameters should be declared
 // using |MOJO_RESTRICT| unless aliasing is explicitly allowed.
 #if defined(__GNUC__) || defined(_MSC_VER)
 // Use |__restrict|, since it works both in C++ and when compiling as C90
 // (|restrict| is only available in C99 and later, and never in C++).
 #define MOJO_RESTRICT __restrict
 #else
 #error "Please define MOJO_RESTRICT for your compiler."
 #endif
 
-#endif  // MOJO_PUBLIC_C_SYSTEM_MACROS_H_
+#endif  // MOJO_PUBLIC_C_INCLUDE_MOJO_MACROS_H_