I was able to run the following to build this morning.

$ ./build.cmd -subset Clr -c Checked
$ ./build.cmd -subset Libs -c Checked

When I tried to run "dotnet" from a library folder, I got this error;

$ dotnet --version
bash: /C/Users/mrj00/source/repos/runtime/artifacts/bin/testhost/netcoreapp5.0-Windows_NT-Debug-x64/dotnet: No such file or directory

I thought the only valid values for -c for the libraries were "Release" and "Debug". So it should not accept "Checked".

So I tried this from the reporoot:

$ ./build.cmd -c Fizzbin

This was accepted. I interrupted the build, and the following folder was found:
artifacts/bin/coreclr/Windows_NT.x64.Fizzbin

I believe that the invalid values for -c should be rejected immediately, rather than appearing to succeed, only to produce difficulties later.