When we create a source tarball, documentation and other generated files
are disted. Those files depend on the configure options when creating
the tarball. For example, the generated man pages contain the compile time
configurable default values.

For that reason, it is generally better to regenerate the documentation when
building NetworkManager. However, let's set explict configure options to
have a more reproducible way to generate the tarball.

When doing a release, you should not just call `make dist`. Instead, the
proper way of creating an official source tarball is:

  $ ./contrib/fedora/rpm/build_clean.sh --srpm