bug#27810: macOS runtime feature detection

[Eli Zaretskii]

> From: Richard Stallman <rms@gnu.org>
> CC: alan@idiocy.org, 27810@debbugs.gnu.org
> Date: Fri, 28 Jul 2017 13:14:19 -0400
> 
>   > AFAIU, cross-compiling Emacs cannot work because building Emacs
>   > includes dumping, which needs to run the produced binary.
> 
> 'make emacs' can't run to completion in a cross-environment, but
> cross-compilation can work well enough in practice.  Precisely, 'make
> temacs' can work with a cross compiler; then you can dump with temacs
> on the target platform.

You'd need to copy the entire build tree to the target platform for
that to work, so it's not really a cross-build anymore, not in the
usual sense.