Ok, after some comments from Nick I looked at it again.

With the current state of config.gcc there is no good way to get what
we want with $target_cpu_default for sparc*. Since this is a lost battle
and we hopefully will get a newer compiler (that does this all different)
sometime soon, how about this patch? It should fix the problem and keep
command line semantics.

Martin

Index: configure.in
===================================================================
RCS file: /cvsroot/src/gnu/dist/gcc/gcc/configure.in,v
retrieving revision 1.4
diff -u -r1.4 configure.in
--- configure.in	10 Feb 2004 12:56:21 -0000	1.4
+++ configure.in	17 Nov 2005 09:13:45 -0000
@@ -880,8 +880,10 @@
 # For the host machine, we save the xm_file variable as host_xm_file;
 # then we decode the target machine and forget everything else
 # that came from the host machine.
+arg_with_cpu="$with_cpu"
 for machine in $build $host $target; do
 	. ${srcdir}/config.gcc
+	with_cpu="$arg_with_cpu"
 done
 
 extra_objs="${host_extra_objs} ${extra_objs}"