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

mojo/public/c/system/tests/compile_unittest_pure_c.c

 // 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.
 
 #ifdef __cplusplus
 #error "This file should be compiled as C, not C++."
 #endif
 
+// Include all the header files that are meant to be compilable as C.
+#include <mojo/macros.h>
 #include <stddef.h>
 #include <string.h>
 
 // Include all the header files that are meant to be compilable as C.
 #include "mojo/public/c/environment/async_waiter.h"
 #include "mojo/public/c/environment/logger.h"
 #include "mojo/public/c/system/buffer.h"
 #include "mojo/public/c/system/data_pipe.h"
 #include "mojo/public/c/system/handle.h"
-#include "mojo/public/c/system/macros.h"
 #include "mojo/public/c/system/main.h"
 #include "mojo/public/c/system/message_pipe.h"
 #include "mojo/public/c/system/result.h"
 #include "mojo/public/c/system/time.h"
 #include "mojo/public/c/system/wait.h"
 #include "mojo/public/c/system/wait_set.h"
 
 // The joys of the C preprocessor....
 #define STRINGIFY(x) #x
 #define STRINGIFY2(x) STRINGIFY(x)
@@ skipping 73 matching lines @@
   EXPECT_EQ((uint32_t)sizeof(kHello), num_bytes);
   EXPECT_EQ(0, memcmp(buffer, kHello, sizeof(kHello)));
 
   EXPECT_EQ(MOJO_RESULT_OK, MojoClose(handle0));
   EXPECT_EQ(MOJO_RESULT_OK, MojoClose(handle1));
 
   // TODO(vtl): data pipe
 
   return NULL;
 }