Abandoned ship, though I remain very very curious how this was considered reasonable by anyone. Though in fairness these days as soon as I see a .yaml file anywhere I tend to go “oh, shit, this is some software with insane build and usage nonsense that only corporate devs think is remotely acceptable”.
Conversely, #StrawberryPerl installed very easily and obviously, and all I needed to do was add its bin folder to my %PATH% et voila, it built the part of PostgreSQL I needed to build just fine.
Seems pretty silly the #PostgreSQL docs recommend, borderline insist, on using ActiveState Perl when Strawberry Perl provides #Perl in a far more “actually provides it to you” way :P