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

mojom/generators/c/templates/header.tmpl.go

 // Copyright 2016 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.
 
 package templates
 
 // TODO(vardhan): Include only the necessary headers for a particular
 // mojom.
 const GenerateHeaderFile = `
 {{- define "GenerateHeaderFile" -}}
 // This file was auto-generated by the C bindings generator.
 
 #ifndef {{.HeaderGuard}}
 #define {{.HeaderGuard}}
 
 #include <assert.h>
 #include <math.h>
+#include <mojo/macros.h>
 #include <stdbool.h>
 #include <stdint.h>
 
 #include "mojo/public/c/bindings/array.h"
 #include "mojo/public/c/bindings/buffer.h"
 #include "mojo/public/c/bindings/interface.h"
 #include "mojo/public/c/bindings/lib/type_descriptor.h"
 #include "mojo/public/c/bindings/map.h"
 #include "mojo/public/c/bindings/string.h"
 #include "mojo/public/c/bindings/validation.h"
 #include "mojo/public/c/system/handle.h"
-#include "mojo/public/c/system/macros.h"
 
 // Imports.
 {{range $import := .Imports -}}
 #include "{{$import}}"
 {{end}}
 
 MOJO_BEGIN_EXTERN_C
 
 // Forward declarations for structs.
 {{range $struct := .Structs -}}
@@ skipping 45 matching lines @@
 {{end}}
 
 // Type tables declarations for structs and unions.
 {{template "GenerateTypeTableDeclarations" .TypeTable}}
 
 MOJO_END_EXTERN_C
 
 #endif  // {{.HeaderGuard}}
 {{- end }}
 `