Toplevel (b-i-b) patch: Clean up CXX_FOR_TARGET

[DJ Delorie]

> Cross-compile worked just fine.  Can I commit now?

Yes.

> I'm also getting an unrelated problem with the rda directory refusing to 
> configure, claiming 'collect-ld: cannot open sim-crt0.o: No such file or 
> directory'.  There's obviously some kind of search patch problem.  But 
> this is while checking for the *C* compiler.

Please bring this up on the gdb mailing list.