diff --git a/eng/Version.Details.xml b/eng/Version.Details.xml
index fee1aa96253a77..61c7149bde78a4 100644
--- a/eng/Version.Details.xml
+++ b/eng/Version.Details.xml
@@ -174,9 +174,9 @@
       <Uri>https://github.com/dotnet/runtime</Uri>
       <Sha>3782e6e41cfaf76ec9ae4117722f835596026b1a</Sha>
     </Dependency>
-    <Dependency Name="Microsoft.NET.ILLink.Tasks" Version="6.0.100-preview.2.21226.1">
+    <Dependency Name="Microsoft.NET.ILLink.Tasks" Version="6.0.100-preview.5.21229.1">
       <Uri>https://github.com/mono/linker</Uri>
-      <Sha>1dfcf3077aca1ea77850f409d95c3192f03507b3</Sha>
+      <Sha>307f6b0afd2fea639fffa97e67155bafe6aa8461</Sha>
     </Dependency>
     <Dependency Name="Microsoft.DotNet.XHarness.TestRunners.Xunit" Version="1.0.0-prerelease.21227.1">
       <Uri>https://github.com/dotnet/xharness</Uri>
diff --git a/eng/Versions.props b/eng/Versions.props
index 456dd679cb894a..cffc176e5cc3b3 100644
--- a/eng/Versions.props
+++ b/eng/Versions.props
@@ -161,7 +161,7 @@
     <!-- Docs -->
     <MicrosoftPrivateIntellisenseVersion>5.0.0-preview-20201009.2</MicrosoftPrivateIntellisenseVersion>
     <!-- ILLink -->
-    <MicrosoftNETILLinkTasksVersion>6.0.100-preview.2.21226.1</MicrosoftNETILLinkTasksVersion>
+    <MicrosoftNETILLinkTasksVersion>6.0.100-preview.5.21229.1</MicrosoftNETILLinkTasksVersion>
     <!-- ICU -->
     <MicrosoftNETCoreRuntimeICUTransportVersion>6.0.0-preview.5.21226.1</MicrosoftNETCoreRuntimeICUTransportVersion>
     <!-- Mono LLVM -->
diff --git a/src/coreclr/System.Private.CoreLib/CreateRuntimeRootILLinkDescriptorFile.targets b/src/coreclr/System.Private.CoreLib/CreateRuntimeRootILLinkDescriptorFile.targets
index aa50f44411c9f3..845e8fccfd8d3c 100644
--- a/src/coreclr/System.Private.CoreLib/CreateRuntimeRootILLinkDescriptorFile.targets
+++ b/src/coreclr/System.Private.CoreLib/CreateRuntimeRootILLinkDescriptorFile.targets
@@ -37,6 +37,7 @@
                                            CortypeFilePath="$(_CortypeFilePath)"
                                            RexcepFilePath="$(_RexcepFilePath)"
                                            ILLinkTrimXmlFilePath="$(_ILLinkDescriptorsIntermediatePath)"
+                                           DefineConstants="$(DefineConstants);FOR_ILLINK"
                                            RuntimeRootDescriptorFilePath="$(_ILLinkRuntimeRootDescriptorFilePath)" />
   </Target>
 
diff --git a/src/coreclr/clr.featuredefines.props b/src/coreclr/clr.featuredefines.props
index 00dbb98bf02d55..dcd11139bfa9e2 100644
--- a/src/coreclr/clr.featuredefines.props
+++ b/src/coreclr/clr.featuredefines.props
@@ -52,7 +52,8 @@
         <DefineConstants Condition="'$(FeatureTypeEquivalence)' == 'true'">$(DefineConstants);FEATURE_TYPEEQUIVALENCE</DefineConstants>
         <DefineConstants Condition="'$(FeatureBasicFreeze)' == 'true'">$(DefineConstants);FEATURE_BASICFREEZE</DefineConstants>
         <DefineConstants Condition="'$(FeaturePortableShuffleThunks)' == 'true'">$(DefineConstants);FEATURE_PORTABLE_SHUFFLE_THUNKS</DefineConstants>
-
+        <DefineConstants Condition="'$(FeatureICastable)' == 'true'">$(DefineConstants);FEATURE_ICASTABLE</DefineConstants>
+        
         <DefineConstants Condition="'$(ProfilingSupportedBuild)' == 'true'">$(DefineConstants);PROFILING_SUPPORTED</DefineConstants>
         <DefineConstants Condition="'$(FeatureProfAttach)' == 'true'">$(DefineConstants);FEATURE_PROFAPI_ATTACH_DETACH</DefineConstants>
     </PropertyGroup>
diff --git a/src/coreclr/vm/corelib.h b/src/coreclr/vm/corelib.h
index c9bc96ccb4e7c4..1821750337f4b9 100644
--- a/src/coreclr/vm/corelib.h
+++ b/src/coreclr/vm/corelib.h
@@ -869,7 +869,7 @@ DEFINE_FIELD_U(_requireWaitNotification, SynchronizationContextObject, _requireW
 DEFINE_CLASS(SYNCHRONIZATION_CONTEXT,    Threading,              SynchronizationContext)
 DEFINE_METHOD(SYNCHRONIZATION_CONTEXT,  INVOKE_WAIT_METHOD_HELPER, InvokeWaitMethodHelper, SM_SyncCtx_ArrIntPtr_Bool_Int_RetInt)
 
-#ifdef _DEBUG
+#ifdef DEBUG
 DEFINE_CLASS(STACKCRAWMARK,         Threading,       StackCrawlMark)
 #endif