JitDiagnosers should print an error when run on non-Windows OS (#1861)

Author: adamsitnik

src/BenchmarkDotNet.Diagnostics.Windows/JitDiagnoser.cs

@@ -3,6 +3,7 @@
 using BenchmarkDotNet.Diagnosers;
 using BenchmarkDotNet.Engines;
 using BenchmarkDotNet.Loggers;
+using BenchmarkDotNet.Portability;
 using BenchmarkDotNet.Reports;
 using BenchmarkDotNet.Running;
 using BenchmarkDotNet.Validators;
@@ -30,7 +31,13 @@ public void Handle(HostSignal signal, DiagnoserActionParameters parameters)
 
         public virtual IEnumerable<Metric> ProcessResults(DiagnoserResults results) => Array.Empty<Metric>();
 
-        public IEnumerable<ValidationError> Validate(ValidationParameters validationParameters) => Array.Empty<ValidationError>();
+        public IEnumerable<ValidationError> Validate(ValidationParameters validationParameters)
+        {
+            if (!RuntimeInformation.IsWindows())
+            {
+                yield return new ValidationError(true, $"{GetType().Name} is supported only on Windows");
+            }
+        }
 
         public void DisplayResults(ILogger outputLogger)
         {