Make cross-compiling temacs easier: drop gnulib for build intermediates, or use recursive autoconf?

[James Luke <james92856@gmail.com>]

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I'm interested in making cross-compilation of emacs easier. Or rather,
making cross-compilation of temacs easier, such that one can run temacs on
the host machine to finish the build. This would make it easier to create
reproducible builds (particularly with Guix/NixOS as the build machine),
and means one doesn't need a C compiler on the host. Right now the problem
I'm running into is caused by build intermediates that must be built then
run on the builder: the programs "lib-src/make-docfile.c" and
"lib-src/make-fingerprint.c".

These intermediates both use gnulib (with #include <config.h> etc), but
configure.ac only configures gnulib for the host machine. So the headers,
#defines, and library are all wrong for the build machine and compilation
fails. To fix this, I'd like to rewrite make-fingerprint.c and
make-docfile.c to avoid non-portable constructs and thus the dependency on
gnulib, but I don't know if this is considered acceptable for a GNU
project. The alternative is a larger overhaul of the build system, with a
nested configure script (to run configure for the builder when doing a
cross build), another makefile, and another gnulib tree (for the modules
needed only for the intermediates). I suspect the latter would be more
fragile and produce a much larger maintenance burden than the former.

Would there be any objections to the simple rewrite?

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