GNU Automake will generate a broken Makefile when configuring if some variables containing line breaks.
Thanks for the report. I'm not sure what Automake can do about it, though. It's just doing what it's been told, seems to me? Admittedly the error message is less than ideal, although the second message /tmp/GmXRgxDy:359: *** missing separator. Stop. is a clue. --best, karl.