Building in .NET Framework 4

It's great that this library supports .NET Framework 4 – that's what makes it superior to System.CommandLine for our use case. However, we've only managed to use the pre-built DLL. When trying to build the project from master with our MSBuild version, it builds nothing and emits this warning:
```
warning MSB4078: The project file "src\CommandLine\CommandLine.csproj" is not supported by MSBuild and cannot be built.
```
Apparently the format of the .csproj file, with ``, is only supported from MSBuild version 15.0 onwards, while the .NET Framework 4 MSBuild version (4.8 in our case) only supports .csproj files with ``.

Has anyone had success building this library under .NET Framework version 4?

Commencez par src\CommandLine\CommandLine.csproj et reproduisez le build avec le .NET Framework MSBuild 4.8 indiqué, en vérifiant l'avertissement MSB4078. Comparez le format du projet avec le format pris en charge par la version de MSBuild ; c'est terminé lorsque la bibliothèque se compile depuis master sous .NET Framework 4 au lieu de nécessiter uniquement la DLL précompilée.

Rédigé par le modèle d'indexation à partir du texte de l'issue.