AC_TRY_RUN and cross-compiling (was: Re: ORBit 0.5.8 Cross-Compile problems...)

[Dan Kegel]

Ossama Othman wrote:
> 
> > > Now, now, it's OK to use AC_TRY_RUN if there's a reasonable fallback
> > > when not cross-compiling.  (Please don't stick pins into my doll's
> > > head!  :-)
> >
> > So YOU'RE the one! :-)  I dare you to show me a reasonable use of
> > AC_TRY_RUN that is correct both for self-hosted and for cross
> > development.
> > (Defaults that work for 'most' targets don't qualify.)
> 
> I have to agree with Paul.  Sometimes it's just not possible to rely
> on compile/link-time tests alone.

That's ok if three things hold:
1. configure.in authors avoid gratuitous use of AC_TRY_RUN.
2. All autoconf macros that use AC_TRY_RUN allow overriding the
   test via environment variables.  (This comes for free if you
   use the cache, I think.)  configure.in authors who write
   custom macros may need education on this.
3. AC_TRY_RUN lets the user specify how to run code on the target,
   e.g. with a --with-target-run=foo.sh option, where foo.sh is
   a script that runs the given command remotely, e.g. via ssh.
   (By default, configure would assume you can't run code on the target
   when cross-compiling, just like now.)

- Dan