canadian vs build==host configury (and $with_cross_host)

[Adam Megacz]

Adam Megacz <megacz@cs.berkeley.edu> writes:
> I think Canadian cross-builds need their own case arm in that block of
> configure.ac (the "we cannot execute the compiler we just built" case,
> which is not identical to the "we are making a cross-compiler" case).

I see there's some code that attempts to do this with $which_gcj.
Unfortunately it relies on $with_cross_host, which does not work
properly for non-canadian (host==build) cross-compiles:

   gcc/configure.in:

   # Passing a --with-cross-host argument lets the target libraries know
   # whether they are being built with a cross-compiler or being built
   # native.  However, it would be better to use other mechanisms to make the 
   # sorts of decisions they want to make on this basis.  Please consider
   # this option to be deprecated.  FIXME.

   if test x${is_cross_compiler} = xyes ; then
     target_configargs="--with-cross-host=${host_alias} ${target_configargs}"
   fi

If you invoke

  ./configure --target=foo

You get

  libgcj/configure --with-cross-host=""

(that is, the empty string).
   
What is the right thing to do here?

  - a