Autoconf variable *manipulation* in .in files?

[Dan Kegel]

I'm writing a build system that places one Make include file
in each directory, and includes them from a single master Makefile
recursively.  It can handle builds for multiple architectures
all in the same run, without recursive invocations of Make.

Along the way, I got a strange craving for being able
to create local tempoarary autoconf variables,
for elimination of common subexpressions that are
too ephemeral to merit mention in configure.ac.

I know, this is getting away from the original autoconf concept
of 'variables are defined in configure.ac, and expanded
in .in files', but it's not *that* far away.

Has anyone else had similar urges?
- Dan