C bindings: Implement _Validate(), and some pre-requisites

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

Index: mojom/generators/c/templates/interface.tmpl.go
diff --git a/mojom/generators/c/templates/interface.tmpl.go b/mojom/generators/c/templates/interface.tmpl.go
index 29f387b8099a7ce5e52e9698201bfc8b05ae0bb8..964a6341f266713e5d575f1d70d6e4b9a30dedab 100644
--- a/mojom/generators/c/templates/interface.tmpl.go
+++ b/mojom/generators/c/templates/interface.tmpl.go
@@ -30,15 +30,11 @@ extern const {{$const.Type}} {{$const.Name}};
 #define {{$interface.Name}}_{{$message.Name}}__MinVersion \
     ((uint32_t){{$message.MinVersion}})
 
-
 struct {{$message.RequestStruct.Name}};
 {{template "GenerateStructDeclarations" $message.RequestStruct}}
 {{if ne $message.ResponseStruct.Name "" -}}
-#define {{$interface.Name}}_{{$message.Name}}__HasResponse 1
 struct {{$message.ResponseStruct.Name}};
 {{template "GenerateStructDeclarations" $message.ResponseStruct}}
-{{else}}
-#define {{$interface.Name}}_{{$message.Name}}__HasResponse 0
 {{end}}
 {{end}}
 {{end}}