Improve output of `/configure --help` for disabled/enabled options by default

[dilyanpalauzov]

./configure --help prints

  --enable-shared[=PKGS]  build shared libraries [default=yes]
  --enable-static[=PKGS]  build static libraries [default=yes]
  --enable-liblsof        build and install liblsof [default=yes]
  --enable-security       allow only the root user to list all open files
                          [default=no]
  --enable-no-sock-security
                          combined with --enable-security, allow anyone to
                          list anyone else's socket files [default=no]

For me, if the --help output contains --enable-Z this means by default Z is disabled. The opposite is also true: if --help prints --disable-Y this means that by default Z is enabled.

Please consider in the above output to remove “ [default=…]" and to substitute the first three enable above with disable.

I have written an article on this: https://ab.bapha.be/posts/help-output/.

[jiegec]

Pull requests are welcome.