I'm running ...

ros install sbcl-bin/2.5.10
ros use sbcl-bin/2.5.10

... on FreeBSD 15.0, per the workaround for #610.

However it seems that this version has been compiled without threads, which in turn causes bordeaux-threads not to install.

This seems to be a regression. I had the same issue some time ago with 2.5.3; #602. It was fixed as of 2.5.4, but seems to be back.