include: Change RPC_STATUS from long to LONG for Win64 compatibility.

Also fix the compiler warnings introduced by this change.
diff --git a/include/rpc.h b/include/rpc.h
index 6c92ecc..3e7e129 100644
--- a/include/rpc.h
+++ b/include/rpc.h
@@ -51,7 +51,7 @@
 #define __RPC_STUB __stdcall
 #define RPC_ENTRY  __stdcall
 #define RPCRTAPI
-typedef long RPC_STATUS;
+typedef LONG RPC_STATUS;
 
 typedef void* I_RPC_HANDLE;