Without the change build fails on upstrem gcc-10 as: ld: proto/.libs/libproto.a(cap.o):/build/source/src/proto/../../src/pkt_source.h:54: multiple definition of `pkt_count'; main.o:/build/source/src/pkt_source.h:54: first defined here
No idea how ever built. TIL about nix-prefetch-url.