Just a thought, would it be simpler to rename VERSION.txt to VERSION instead of changing the references? I think that would require fewer code changes and it matches upstream libpcap convention.

That would work on most Linux systems and match the upstream libpcap convention, but it wouldn’t help on macOS because the filesystem is case-insensitive. This causes issues like the one described in Issue #2747.

For fewer code changes, it could be possible to include

mv VERSION VERSION.txt
sed -i '' 's/VERSION/VERSION.txt/g' ./Makefile.in

in libpcap/configure or something and make it automated on specific systems, but I haven't thought it through properly.
Which would make a git diff every time I guess...

That would work on most Linux systems and match the upstream libpcap convention, but it wouldn’t help on macOS because the filesystem is case-insensitive. This causes issues like the one described in Issue #2747.

Unless it is built with a MacOS Case Sensitive file system. The OS supports both.

Updated comment here:
#3158 (comment)