chore(.gitignore): add more autotool files

[akinomyoga]

The filenames compfile, depcomp, ltmain.sh, and config.{guess,sub} are added in .gitignore. Also, I collected the autotool-related entries in a section.

[scop]

I've nothing against this in principle, but I'd like to understand which versions or scenarios cause the files compile, depcomp, config.guess, config.sub, and ltmain.sh to appear. They do not for me in Ubuntu 20.04 or Fedora dev, autoreconf -i; ./configure; make.

[akinomyoga]

Ah, OK. I do somehow have these files but couldn't reproduce them in a clean bash-completion repository (with autotools from Fedora 36), but now I have identified why I have these files. To investigate the historical behavior of cryptsetup --help & man cryptsetup for #759, I cloned a repository of cryptsetup in a subdirectory and tried to build it. It somehow seems to create the related files at an upper level. In short, I could reproduce them by the following steps.

bash-completion$ git clone git@gitlab.com:cryptsetup/cryptsetup.git
bash-completion$ cd cryptsetup
cryptsetup$ ./autogen.sh

Running autoreconf -i in the cryptsetup directory instead of autogen.sh also rewrites the files of the parent directory. I did not know autoreconf -i could rewrite the files outside the directory.

[akinomyoga]

OK, I think there is no reason to add these files created by autoreconf -i of external projects in .gitignore. I just dropped these files. I keep this PR open as it still has some changes though it is now reduced to just a cosmetic update.

[scop]

Thanks!