Version 1.126 of libstdc++-v3/configure.in broke pre-installed newlib builds

[Hans-Peter Nilsson]

Hi Ben.  Your change 1.126 to libstdc++-v3/configure.in:

        PR libstdc++/3066.
         * configure.in: Switch target to host, don't assume newlib.
         (target_alias): Remove.
         * configure: Regenerate.
         * acinclude.m4: Same.
         * aclocal.m4: Regenerate.
         * configure.target: Same. Rename to...
         * configure.host: This.

broke builds where newlib is *pre-installed* (i.e. $with_newlib
!= yes actually), for example as in my cris-axis-elf test-setup:

...
configure: error: No support for this host/target combination.
make[1]: *** [configure-target-libstdc++-v3] Error 1

Suggestion for a fix?  What was wrong with assuming newlib for
the default case of a cross-build (as in not matched by the
other cases in that switch-statement)?  The PR doesn't seem to
be opposed to that.  At least newlib could be assumed for an
otherwise unmatched target (sorry, that should be "host" ;-)
matching *-*-elf*.  Or if these simple solutions aren't to
taste, I could cook up an autoconf test for an installed newlib.

brgds, H-P