bug#9192: Cross-compile for ARM

[Stefan Monnier <monnier@iro.umontreal.ca>]

> Is it a 'feature' or is it a bug?

It's not a feature, but it's not a bug we find very important to fix.
IOW I'd be happy to accept patches which make cross-compiling easier,
but I won't write them myself and I would only accept them if they're
clean enough.

This said, I do remember someone posting on this list about a similar
issue and making actual progress in this direction.  And if you want to
try it, here are some things I know will need to be solved:
- We build a few programs used only during compilation: prefix-args,
  make-docfile, probably a few more (can't remember test-distrub, but
  if we build such a thing, then it's most likely in the set as well).
  You'll have to change the Makefile to compile those for the host
  rather than for the target.
- The Elisp files in lisp and leim need to be compiled by Emacs, so the
  src/bootstrap-emacs should be built for the host rather than for
  the target.
- You'll either want to build without dumping (i.e. set CANNOT_DUMP), or
  you'll want to split the dump step since it needs to be run on the
  target (but in either case you can do the dump for src/bootstrap-emacs
  since that runs on the host).  Builds using CANNOT_DUMP tend to have
  various misfeatures because this is basically never used and hence
  doesn't get much/any testing.

Maybe the easiest way to approach the problem is to first do a normal
build on the host (which builds src/bootstrap-emacs and compiles all the
Elisp files), then "rm src/*.o", reconfigure for the target and compile
src/temacs (and maybe afterwards do the `dump' on the target).


        Stefan