in reply to "make test" catches a C undefined symbol, but "prove" doesn't

Ok, so it turns out after some searching that I needed to build against the rt library as in add it to the LIBS aref in my Makefile.PL:

LIBS => ['-lwiringPi -lwiringPiDev -lrt'],

After I added that, make test does The Right Thing (no more error about shm_open() being an undefined symbol.

I'm going to do some research as to how prove doesn't break, and if nobody else has an answer by then, I'll update here for completeness.