d/rules: fix ftbfs in gnulib progname (Closes: #1129132)

the copied-in progname.c program relies on gnulib's memeq. replace it by !memcmp.

• debian bug: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1129132
• launchpad bug: https://bugs.launchpad.net/ubuntu/+source/libpaper/+bug/2146894