Added support for tests to check if they are running under the mono i…

…nterpreter (dotnet#33106)

The mono interpreter is activated by passing --interpreter into the MONO_ENV_OPTIONS
environment variable.

src/libraries/Common/tests/CoreFx.Private.TestUtilities/System/PlatformDetection.cs

@@ -20,6 +20,7 @@ public static partial class PlatformDetection
 
         public static bool IsNetCore => RuntimeInformation.FrameworkDescription.StartsWith(".NET Core", StringComparison.OrdinalIgnoreCase);
         public static bool IsMonoRuntime => Type.GetType("Mono.RuntimeStructs") != null;
+        public static bool IsMonoInterpreter => GetIsRunningOnMonoInterpreter();
         public static bool IsFreeBSD => RuntimeInformation.IsOSPlatform(OSPlatform.Create("FREEBSD"));
         public static bool IsNetBSD => RuntimeInformation.IsOSPlatform(OSPlatform.Create("NETBSD"));
 
@@ -201,5 +202,13 @@ private static bool GetSsl3Support()
 
             return (IsOSX || (IsLinux && OpenSslVersion < new Version(1, 0, 2) && !IsDebian));
         }
+
+        private static bool GetIsRunningOnMonoInterpreter()
+        {
+            // This is a temporary solution because mono does not support interpreter detection
+            // within the runtime.  
+            var val = Environment.GetEnvironmentVariable("MONO_ENV_OPTIONS");
+            return (val != null && val.Contains("--interpreter"));
+        }
     }
 }