title: Embedding C# sources in PDB with new csproj
body: <p>The recently-released .NET tooling seem to have support for <a href="https://github.com/dotnet/roslyn/pull/12353" rel="noreferrer">embedding C# in PDBs</a>, which should improve the experience of stepping into third-party, etc. Running <code>csc /?</code>, I can clearly see the /embed option: "Embed all source files in the PDB."</p>
  
  <p>However, there doesn't seem to be any way to specify this in csproj. What's more, there doesn't seem to be any provisions for passing arbitrary switches to the compiler, which I would use to manually pass /embed.</p>
  
  <p>Can anyone confirm that I haven't missed anything and that build support for /embed is currently lacking? Is there an issue for this (and if not where would it go)? Any suggested workaround would be appreciated too.</p>