The "script" I had in mind is just a sed one-liner, based on Neil's own suggestion from a while back:
$ sed -e "s/(.)(.)(.)/\1.\2.\3/" < ~/merc/scintilla/version.txt
With all due respect to Neil, is he guaranteeing there will not be a 5.1.10, its up to 5.1.6 already? Remember as I pointed out there was a 3.21.1.
To be clear, I do not want it part of configure or make, it is something that changes once when Scintilla changes and there is a shell script `update-scintilla.sh` to run when doing that upgrade, thats the correct place to do it.
When importing Scintilla and Lexilla `version.txt` convert to a string literal with the dots and import it as @kugel- showed above. Can even write to a `version.h` file if you don't want to change `version.txt`