No PPA dbgsym packages

[Jan Wielemaker]

I'm faced with a user bug report against https://launchpad.net/~swi-prolog/+archive/ubuntu/devel
So far, no matter what I do I failed to reproduce the problem using a locally built executable. Unfortunately, the advice on https://wiki.ubuntu.com/DebuggingProgramCrash results in the claim that
`main/debug` doesn't exist. But, the log file claims `DEB_BUILD_OPTIONS=noautodbgsym parallel=4`, which suggests that debug packages are not built by default, although that is claimed to be the case.

So, I edited `rules` to state `DEB_BUILD_OPTIONS parallel=4`. This produces some messages about debug packages being built in e.g., https://launchpadlibrarian.net/376831676/buildlog_ubuntu-bionic-amd64.swi-prolog_7.7.17-4-g8c67c404a-bionicppa2_BUILDING.txt.gz, but still no debug packages.

Any clue what is wrong?