Log an error message when the profiler is loaded multiple times

tracer/src/Datadog.Tracer.Native/cor_profiler.cpp

@@ -51,6 +51,13 @@ HRESULT STDMETHODCALLTYPE CorProfiler::Initialize(IUnknown* cor_profiler_info_un
         Logger::EnableDebug(true);
     }
 
+    if (profiler != nullptr)
+    {
+        Logger::Error("The Tracer Profiler is initialized multiple times. This may cause unpredictable failures.",
+            " When running aspnetcore in IIS, make sure to disable managed code in the application pool settings.",
+            " https://learn.microsoft.com/en-us/aspnet/core/host-and-deploy/iis/advanced?view=aspnetcore-9.0#create-the-iis-site");
+    }
+
     CorProfilerBase::Initialize(cor_profiler_info_unknown);
 
     // we used to bail-out if tracing was disabled, but we now allow the tracer to be loaded