Support WSL detection in RuntimeInformation

Author: AndreyAkinshin

src/BenchmarkDotNet/Portability/RuntimeInformation.cs

@@ -185,14 +185,30 @@ public static string GetOsVersion()
                 return null;
             try
             {
-                return LinuxOsReleaseHelper.GetNameByOsRelease(File.ReadAllLines("/etc/os-release"));
+                string version = LinuxOsReleaseHelper.GetNameByOsRelease(File.ReadAllLines("/etc/os-release"));
+                bool wsl = IsUnderWsl();
+                return wsl ? version + " WSL" : version;
             }
             catch (Exception)
             {
                 return null;
             }
         }
 
+        private static bool IsUnderWsl()
+        {
+            if (!IsLinux())
+                return false;
+            try
+            {
+                return File.Exists("/proc/sys/fs/binfmt_misc/WSLInterop"); // https://superuser.com/a/1749811
+            }
+            catch (Exception)
+            {
+                return false;
+            }
+        }
+
         // TODO: Introduce a common util API for registry calls, use it also in BenchmarkDotNet.Toolchains.CsProj.GetCurrentVersionBasedOnWindowsRegistry
         /// <summary>
         /// On Windows, this method returns UBR (Update Build Revision) based on Registry.