Add custom logic for reflection-emit to RemoveFeaturesStep. (dotnet#590)

* Add custom logic for reflection-emit to RemoveFeaturesStep.

When `--exclude-feature sre` is provided, then we rewrite the
`System.RuntimeType.MakeTypeBuilderInstantiation` to throw.

* Address cosmetic feedback.

src/linker/Linker.Steps/RemoveFeaturesStep.cs

@@ -12,6 +12,7 @@ public class RemoveFeaturesStep : BaseStep
 
 		public bool FeatureCOM { get; set; }
 		public bool FeatureETW { get; set; }
+		public bool FeatureSRE { get; set; }
 
 		//
 		// Manually overrides System.Globalization.Invariant mode
@@ -57,6 +58,17 @@ void ProcessType (TypeDefinition type)
 					ExcludeEventSourceImplementation (type);
 			}
 
+			if (FeatureSRE) {
+				if (type.Namespace == "System" && type.Name == "RuntimeType") {
+					foreach (var method in type.Methods) {
+						if (method.Name == "MakeTypeBuilderInstantiation") {
+							Annotations.SetAction (method, MethodAction.ConvertToThrow);
+							break;
+						}
+					}
+				}
+			}
+
 			if (RemoveCustomAttributes (type)) {
 				if (FeatureCOM && type.IsImport) {
 					type.IsImport = false;

src/linker/Linker/Driver.cs

@@ -353,6 +353,7 @@ public void Run (ILogger customLogger = null)
 					p.AddStepBefore (typeof (MarkStep), new RemoveFeaturesStep () {
 						FeatureCOM = excluded_features.Contains ("com"),
 						FeatureETW = excluded_features.Contains ("etw"),
+						FeatureSRE = excluded_features.Contains ("sre"),
 						FeatureGlobalization = excluded_features.Contains ("globalization")
 					});