The distributed form of a project (especially one based on GNU autotools) is often not merely a tarball of the upstream repository. Often the author has pre-run some stages of the build that she feels would impose unnecessary or esoteric dependencies. Typically this involves pre-generating Makefile.in from Makefile.am and configure from configure.ac. Another common one is for the maintainer to pre-generate the docume…
https://www.gnu.org/prep/standards/standards.html#Standard-T...