redo is mentioned elsewhere in this very discussion.

One of the things that Daniel J. Bernstein did in his packages is merge steps two and three. There would be makefile/redo rules for detecting the presence of operating-system-specific stuff, and linking the appropriate source/header files into place.

Here's an example from ucspi-tcp that auto-configures whether the platform supports waitpid():

* https://github.com/comotion/ucspi-tcp/blob/master/Makefile#L...

* https://github.com/comotion/ucspi-tcp/blob/master/choose.sh

* https://github.com/comotion/ucspi-tcp/blob/master/trywaitp.c

* https://github.com/comotion/ucspi-tcp/blob/master/haswaitp.h...

* https://github.com/comotion/ucspi-tcp/blob/master/haswaitp.h...

When I extended redo to the whole of djbwares, this system was fairly simple to convert. Here is haswaitp.h.do which is what redo ends up running whenever something reveals a dependency from haswaitp.h :

    #!/bin/sh -e
    redo-ifchange trywaitp.c compile link
    if ( ./compile trywaitp.o trywaitp.c trywaitp.d && ./link trywaitp trywaitp.o ) >/dev/null 2>&1
    then
            echo \#define HASWAITPID 1 > "$3"
    else
            echo '/* sysdep: -waitpid */' > "$3"
    fi

* http://jdebp.eu./Softwares/djbwares/