I found the problem and it should now be fixed in blead. Unfortunately, too late for 5.11.2, but with a monthly release cycle, we'll soon be back on track.
When dual-core modules moved to the cpan/ directory in the Perl source tree, the idea was in part that updating them would be a matter of just unpacking the latest tarball into that directory and deleting stuff that didn't need to be in core. Unfortunately, that doesn't work for Module::Build because Module::Build::ConfigData is dynamically generated, which I forgot when updating blead. Compounding that, the *old* ConfigData file was never moved from the lib/ directory when the powers-that-be moved M::B to the cpan/ directory, so it was still hanging around, with the old *optional features" definitions. Had it it been moved and then I blew it away, git would have warned me it was missing. So two or three small human error all compounded to create this glitch. Nevertheless, as the person doing the blead update, I take responsibility for the end result. I'm going to automate the "update blead" process so this sort of person-at-keyboard error doesn't happen again. Andreas -- thank you for reporting the problem. To everyone - my apologies for screwing this up. David
