[...]
It is straightforward to achieve a similar result with a portable makefile
by using a dedicated witness file, for example (totally untested):

   configure.stamp: configure.ac
         autoconf -o configure.new
        cmp configure.new configure >/dev/null 2>&1 \
          || mv -f configure.new configure
        echo >configure.stamp

   configure: configure.stamp

First of all, thanks to Nick Bowler and Ben Boeckel for the extra information. 
I suspected that something like that should be doable, but I did not have the 
right details.


As Nick says you can get something "kinda-sorta" similar with "witness"
files (I call these "sentinel" files but there's no one accepted term
that I'm aware of).  This does work, if you get it right, but there are
some mildly annoying UI/QoI issues you have to be willing to live with.

Would you care to elaborate about those "UI/QoI issues"?

I am no expert in this regard, but it looks doable. After all, 
Autoconf/Automake completely control the makefile generation and the tools 
which trigger a rebuild of 'configure' and 'Makefile' when you modify 
configure.ac and Makefile.am. If implemented correctly, the user wouldn't 
really notice, or have I missed something?

Regards,
  rdiez

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