Building a second time with a different output directory doesn't work

Building like this:

> dotnet build
> dotnet build -o elsewhere

doesn't work correctly.

Unit test: https://github.com/rolfbjarne/xamarin-macios/commit/f042aeacb32dab4bc9c82f00d6c2c181da02f8ec
Log: [log.txt.zip](https://github.com/xamarin/xamarin-macios/files/10179302/log.txt.zip)

Reproduce the two commands shown: run `dotnet build`, then `dotnet build -o elsewhere`, and compare the result with the attached log. Review the unit test referenced by commit f042aeacb32dab4bc9c82f00d6c2c181da02f8ec. Done means the second build works correctly with a different output directory and the unit test passes.

Written by the indexing model from the issue text.