I got this error when building:
Scrt1.o: in function `_start': undefined reference to `main'
Which led me to this answer: https://stackoverflow.com/a/18825898
I modified my Makefile thusly:
to
$(CC) -shared -o uncom uncom.o
This allowed it to build on my system.
After running config.pl again, the change was overwritten, but compilation succeeded anyway because make or gcc seemed to lazily reuse the files from last time. I don't think modifying the Makefile is the right way to do it, but I couldn't figure out how to modify the perl script to correct the root of the problem.