add Armv6 and Ppc64le architectures support (dotnet#2219)

src/BenchmarkDotNet/Environments/Platform.cs

@@ -40,6 +40,16 @@ public enum Platform
         /// <summary>
         /// LOONGARCH64
         /// </summary>
-        LoongArch64
+        LoongArch64,
+
+        /// <summary>
+        /// A 32-bit ARMv6 processor architecture.
+        /// </summary>
+        Armv6,
+
+        /// <summary>
+        /// A PowerPC 64-bit (little-endian) processor architecture.
+        /// </summary>
+        Ppc64le,
     }
 }

src/BenchmarkDotNet/Portability/RuntimeInformation.cs

@@ -263,11 +263,13 @@ internal static Runtime GetCurrentRuntime()
 
         public static Platform GetCurrentPlatform()
         {
-            // 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
+            // these are not part of .NET Standard 2.0, so we use hardcoded values taken from
+            // https://github.com/dotnet/runtime/blob/1a37caf773a3b857ccff49a31be3333d4fdc491f/src/libraries/System.Private.CoreLib/src/System/Runtime/InteropServices/Architecture.cs#L9
             const Architecture Wasm = (Architecture)4;
             const Architecture S390x = (Architecture)5;
             const Architecture LoongArch64 = (Architecture)6;
+            const Architecture Armv6 = (Architecture)7;
+            const Architecture Ppc64le = (Architecture)8;
 
             switch (ProcessArchitecture)
             {
@@ -285,6 +287,10 @@ public static Platform GetCurrentPlatform()
                     return Platform.S390x;
                 case LoongArch64:
                     return Platform.LoongArch64;
+                case Armv6:
+                    return Platform.Armv6;
+                case Ppc64le:
+                    return Platform.Ppc64le;
                 default:
                     throw new ArgumentOutOfRangeException();
             }