java/5688: cross compiler build fails in libjava

[H.J. Lu]

http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gcc&pr=5688

Is anyone working on this bug? I guess the first thing should be done is 
to change

if test -n "${with_cross_host}"; then
   # We are being configured with a cross compiler.  AC_REPLACE_FUNCS
   # may not work correctly, because the compiler may not be able to
   # link executables.

   # We assume newlib.  This lets us hard-code the functions we know
   # we'll have.
   AC_DEFINE(HAVE_MEMMOVE)
 .....

to something similar in the toplevel configure.in which checks if newlib 
is used
before blindly assuming we are compiling for newlib.