add S390x architecture support (#1712)

Author: adamsitnik

src/BenchmarkDotNet/Environments/Platform.cs

@@ -30,6 +30,11 @@ public enum Platform
         /// <summary>
         /// Wasm
         /// </summary>
-        Wasm
+        Wasm,
+
+        /// <summary>
+        /// S390x
+        /// </summary>
+        S390x
     }
 }

src/BenchmarkDotNet/Extensions/ConfigurationExtensions.cs

@@ -20,6 +20,8 @@ public static string ToConfig(this Platform platform)
                     return "ARM";
                 case Platform.Arm64:
                     return "ARM64";
+                case Platform.S390x:
+                    return "S390x";
                 default:
                     return "AnyCPU";
             }

src/BenchmarkDotNet/Portability/RuntimeInformation.cs

@@ -233,9 +233,10 @@ internal static Runtime GetCurrentRuntime()
 
         public static Platform GetCurrentPlatform()
         {
-            // it's not part of .NET Standard 2.0, so we use a hack
-            // https://github.com/dotnet/runtime/blob/2c573b59aaaf3fd17e2ecab95ad3769f195d2dbc/src/libraries/System.Runtime.InteropServices.RuntimeInformation/src/System/Runtime/InteropServices/RuntimeInformation/Architecture.cs#L12
+            // these are not part of .NET Standard 2.0, so we use a hack
+            // https://github.com/dotnet/runtime/blob/d81ad044fa6830f5f31f6b6e8224ebf66a3c298c/src/libraries/System.Runtime.InteropServices.RuntimeInformation/src/System/Runtime/InteropServices/RuntimeInformation/Architecture.cs#L12-L13
             const Architecture Wasm = (Architecture)4;
+            const Architecture S390x = (Architecture)5;
 
             switch (ProcessArchitecture)
             {
@@ -249,6 +250,8 @@ public static Platform GetCurrentPlatform()
                     return Platform.X86;
                 case Wasm:
                     return Platform.Wasm;
+                case S390x:
+                    return Platform.S390x;
                 default:
                     throw new ArgumentOutOfRangeException();
             }