[DiapDealer]

I don't think it has anything to do with Sigil already being installed. Sigil will happily build and install over a previous installation (or beside one) with no errors. There may be runtime errors in that situation, but not build-time ones. And anyway.... you indicated that the error happens when running the "make" command (and that's a linker error I see). Something else is going on.

You're not trying to build 0.9.13 in the old 0.9.12's build directory, are you? The cmake configure command should be run in an empty directory. Clean out your build directory completely and start with the cmake configure command again.

EDIT: it also looks like you're using a non-repo version of Python3 (3.7.x) on your Bionic system. Did you build Sigil 0.9.12 against that same custom python, or was 0.9.12 built against the system python3 (3.6.x I think). The addon Python 3.7 could be part of the problem if it wasn't built with the necessary options.