I recently read that "There are several ways to configure and build a project using Autotools."
Among them:
Autoconf and Autoscan:
- Makefile.in with project build rules and Makefile substitutions
Autoheader (usable in addition to all other tools)
- scans the project and generates a config.h file during project
configuration with platform specific macro definitions, no configuration
files needed
How do you build a project without "Makefile.am"? Just using Autoconf, Autoscan & maybe Autoheader.
As the link says, Makefile.in is the template for Makefile which would just have @FOO@ macros for configure (via AC_CONFIG_FILES) to substitute. If the project is really simple, I can imagine it would work OK without automake.
All autoscan and autoheader do is help you build primitive configure.ac and config.h files for your project. You aren't required to use them either.