Fix windows build break caused by missing mp_decl

Signed-off-by: Gavin Halliday <gavin.halliday@lexisnexis.com>

system/mp/mpbase.hpp

@@ -138,7 +138,7 @@ extern mp_decl IGroup *createIGroup(const char *endpointlist,unsigned short defp
 extern mp_decl IGroup *deserializeIGroup(MemoryBuffer &src); 
 
 extern mp_decl INode *queryNullNode(); 
-extern INode * queryMyNode();
+extern mp_decl INode * queryMyNode();
 extern mp_decl void initMyNode(unsigned short port);
 
 // Exceptions