Allow reflecting on DebuggableAttribute on CoreRT (#1055)

* Allow reflecting on DebuggableAttribute on CoreRT

See dotnet/corert#6955 (comment).

BenchmakeDotNet reflects on this attribute here:

https://github.com/dotnet/BenchmarkDotNet/blob/a76f438a81e3e0235a2e9b1249a5280038189689/src/BenchmarkDotNet/Extensions/AssemblyExtensions.cs#L28-L38

* Comment

src/BenchmarkDotNet/Toolchains/CoreRt/Generator.cs

@@ -175,7 +175,8 @@ private string GenerateProjectForLocalBuild(BuildPartition buildPartition, Artif
 </Project>";
 
         /// <summary>
-        /// mandatory to make it possible ot call GC.GetAllocatedBytesForCurrentThread() using reflection (not part of .NET Standard)
+        /// mandatory to make it possible to call GC.GetAllocatedBytesForCurrentThread() using reflection (not part of .NET Standard)
+        /// and DebuggableAttribute.
         /// </summary>
         private void GenerateReflectionFile(ArtifactsPaths artifactsPaths)
         {
@@ -184,6 +185,7 @@ private void GenerateReflectionFile(ArtifactsPaths artifactsPaths)
     <Application>
         <Assembly Name=""System.Runtime"">
             <Type Name=""System.GC"" Dynamic=""Required All"" />
+            <Type Name=""System.Diagnostics.DebuggableAttribute"" Dynamic=""Required All"" />
         </Assembly>
     </Application>
 </Directives>
@@ -192,4 +194,4 @@ private void GenerateReflectionFile(ArtifactsPaths artifactsPaths)
             File.WriteAllText(Path.Combine(Path.GetDirectoryName(artifactsPaths.ProjectFilePath), "rd.xml"), content);
         }
     }
-}
+}