Suppress warnings on HP aCC

[SVN r16515]

test/stateless_test.cpp

@@ -24,6 +24,7 @@ struct stateless_integer_add {
   void* operator new(std::size_t, stateless_integer_add*)
   {
     throw std::runtime_error("Cannot allocate a stateless_integer_add");
+    return 0; // suppress warnings
   }
 
   void operator delete(void*, stateless_integer_add*)