This assembly really doesn't matter for nullability, as it's only meant to be used with C++/CLI and only by infrastructure. There's also no annotations necessary on any of the contained attributes, as they are either parameterless or take a parameter that shouldn't be null. Even so, we may as well mark the assembly as being annotated, so that its status is appropriately reflected by tools.
Commit migrated from https://github.com/dotnet/corefx/commit/
57e30310253d9c720722f4363fb75e7df93efa67
<Project Sdk="Microsoft.NET.Sdk">
<PropertyGroup>
+ <Nullable>enable</Nullable>
<Configurations>netcoreapp-Debug;netcoreapp-Release</Configurations>
</PropertyGroup>
<ItemGroup>
<Project Sdk="Microsoft.NET.Sdk">
<PropertyGroup>
<AssemblyName>System.Runtime.CompilerServices.VisualC</AssemblyName>
+ <Nullable>enable</Nullable>
<Configurations>netcoreapp-Debug;netcoreapp-Release</Configurations>
</PropertyGroup>
<!-- Shared CoreCLR -->