Quote

dpkg-shlibdeps: warning: package could avoid a useless dependency if debian/doomseeker/usr/lib/x86_64-linux-gnu/libwadseeker.so.1.2 
was not linked against libpthread.so.0 (it uses none of the library's symbols)

1. Install debuild and dh_make on Debian: apt install devscripts dh-make # as superuser
   
2. Retrieve a Mercurial snapshot of Doomseeker code, at (currently) latest commit a9995252fabcdd532cddcb763dc6c0931510e056 (or earlier). (hg clone'https://bitbucket.org/doomseeker/doomseeker [^]' && hg checkout a9995252fabcdd532cddcb763dc6c0931510e056) # URL must be all lowercase, else Bitbucket may throw HTTPS errors from command line use. wtf?
   
3. Make a tarball release: (cd releasescripts/ && sh ./makesourcepackages.sh --no-sign) # yes, it's silly and requires to change directory first because it looks for ../src/*
   
4. Extract the new source package somewhere: mkdir -p /tmp/doomseeker-debian && tar xfvJ doomseeker-1.2.tar.xz -C /tmp/doomseeker-debian # GNU TAR
   
5. Change directory: cd /tmp/doomseeker-debian/doomseeker-1.2/
   
6. Create stub Debian packaging files for the next step (accepting single package and any details): dh_make -f ../doomseeker-1.2.tar.xz
   
7. Run debuild: debuild -us -uc
   
8. Wait. Eventually debuild warns about dpkg-shlibdeps near the end of compilation, before lintian warnings/errors. (Perhaps ignore lintian for now, using dh_make without changes generates lots of warnings.)