So, please explain to me how (or rather, why you wrongly think that) "It should Just Work."? How could it possibly know to use files, that I've chosen the names for?

Because WriteMakefile() does the remapping internally, to cope with the vagaries of compiler and linker idiosyncracies. Had you read the documentation to which I linked, you wouldn't be asking this question.

Right, so libpq is hardcoded into the LIBS key's value.

Look again. No it isn't. If it was, I wouldn't have had to post my question.

Okay, so I wrote libpq when I meant to say -lpq is, jeez, cut me some slack. Are you being deliberately obtuse? I thought it was obvious that you had to change that part with an interpolation of either -lpq or -lpq64 depending on the result of some platform test (of which I incorrectly assumed you were a past master).

See: ["-L$POSTGRES_LIB -lpq -lm"]--libpq is NOT MENTIONED! -lpq is there (along with -lm, whatever that is?), but not libpq.

And to think you were almost there.

I was hoping that someone who has been through the problem would point me in the right direction, rather than just random guesses.

There was nothing random, nor were they guesses, and I pointed you in precisely the correct direction. I know this stuff. I admit to being a bit light on specific details; I thought you would have been smart enough to fill in the blanks. You're not exactly a newbie, otherwise I would have filled in more blanks for you.

At this point, your replies have done exactly zero to assist me, but given their plausible and somewhat dismissive tone, have probably prevented others from actively considering the problems.

I'll keep that in mind next time.