src: don't mark addon_register_func as dllimport

addon_register_func and its cousin addon_context_register_func are type
definitions, dllimport and dllexport are name mangling directives, i.e.
they're quite unrelated concepts.  MinGW complains about mixing them
when cross-compiling native add-ons.

Signed-off-by: Trevor Norris <trev.norris@gmail.com>
Signed-off-by: Bert Belder <bertbelder@gmail.com>

src/node.h

@@ -203,11 +203,11 @@ NODE_EXTERN v8::Local<v8::Value> WinapiErrnoException(int errorno,
 const char *signo_string(int errorno);
 
 
-NODE_EXTERN typedef void (*addon_register_func)(
+typedef void (*addon_register_func)(
     v8::Handle<v8::Object> exports,
     v8::Handle<v8::Value> module);
 
-NODE_EXTERN typedef void (*addon_context_register_func)(
+typedef void (*addon_context_register_func)(
     v8::Handle<v8::Object> exports,
     v8::Handle<v8::Value> module,
     v8::Handle<v8::Context> context);