Report underlying error when dlopen fails in listcomponents

When dlopen files in listcomponents.exe, listcomponents
prints only that the library didn't load, but doesn't
include information on the underlying error. This change
adds the result of dlerror to the error message.

See merge request !159

GaudiPluginService/src/listcomponents.cpp

@@ -108,7 +108,8 @@ int main(int argc, char* argv[]) {
                     << std::endl;
       }
     } else {
-      std::cerr << "ERROR: failed to load " << lib << std::endl;
+      std::cerr << "ERROR: failed to load " << lib
+                << ": " << dlerror() << std::endl;
       return EXIT_FAILURE;
     }
   }