Diagnose crossgen failures in Microsoft.CodeAnalysis.LanguageServer + Re-enable

[mmitche]

R2R was disabled as part of dotnet/dotnet#3995. After resolving the issue with crossgen, we'll need to re-enable crossgen: dotnet/dotnet#4043 originally reverted this.

See dotnet/dotnet#4061 for links to builds.

[agocke]

@jkoritzinsky Can you take a look at this?

[jkoritzinsky]

Looks like the exit code is 57005, which from what I can tell is the exit code from Windows when a CFG violation is encountered.

I also validated with a non-NativeAOT crossgen2 and there's no failures there.

I'll see if I can get a reproducing build