Discourage using explicit package references to ILCompiler to publish

src/coreclr/nativeaot/BuildIntegration/Microsoft.DotNet.ILCompiler.SingleEntry.targets

@@ -41,6 +41,7 @@
     <_PackageReferenceExceptILCompiler Include="@(PackageReference)" Exclude="Microsoft.DotNet.ILCompiler" />
     <_ILCompilerPackageReference Include="@(PackageReference)" Exclude="@(_PackageReferenceExceptILCompiler)" />
     <KnownILCompilerPack Update="Microsoft.DotNet.ILCompiler" Condition="@(_ILCompilerPackageReference->'%(Identity)')=='Microsoft.DotNet.ILCompiler'">
+        <Warning Text="Adding an explicit package reference to 'Microsoft.DotNet.ILCompiler' works only on a narrow set of scenarios and can run into version errors if not properly used." />
         <ILCompilerPackVersion>@(_ILCompilerPackageReference->'%(Version)')</ILCompilerPackVersion>
     </KnownILCompilerPack>
   </ItemGroup>

src/coreclr/nativeaot/docs/compiling.md

@@ -2,8 +2,7 @@
 
 Please consult [documentation](https://docs.microsoft.com/dotnet/core/deploying/native-aot) for instructions how to compile and publish application.
 
-The rest of this document covers advanced topics only.
-
+The rest of this document covers advanced topics only. Adding an explicit package references to 'Microsoft.DotNet.ILCompile' can generate warnings when publishing and is only supported on a narrow set of scenarios. When possible, use the SDK options to publish a native AOT application.
 
 ## Using daily builds
 
@@ -34,7 +33,7 @@ or by adding the following element to the project file:
 
 ## Cross-architecture compilation
 
-Native AOT toolchain allows targeting ARM64 on an x64 host and vice versa for both Windows and Linux. Cross-OS compilation, such as targeting Linux on a Windows host, is not supported. To target win-arm64 on a Windows x64 host, in addition to the `Microsoft.DotNet.ILCompiler` package reference, also add the `runtime.win-x64.Microsoft.DotNet.ILCompiler` package reference to get the x64-hosted compiler:
+Native AOT toolchain allows targeting ARM64 on an x64 host and vice versa for both Windows and Linux and is now supported in the SDK. Cross-OS compilation, such as targeting Linux on a Windows host, is not supported. To target win-arm64 on a Windows x64 host on an advanced scenario where the SDK support is not sufficient, in addition to the `Microsoft.DotNet.ILCompiler` package reference, also add the `runtime.win-x64.Microsoft.DotNet.ILCompiler` package reference to get the x64-hosted compiler:
 ```xml
 <PackageReference Include="Microsoft.DotNet.ILCompiler; runtime.win-x64.Microsoft.DotNet.ILCompiler" Version="7.0.0-preview.2.22103.2" />
 ```