Add --with-relocated-sources configure option

[Tom Tromey]

>>>>> "Joseph" == Joseph S Myers <joseph@codesourcery.com> writes:

Joseph> +AC_ARG_WITH(relocated-sources,
Joseph> +[  --with-relocated-sources=path    Automatically relocate this path for source files],

I'd prefer it if all new options use AC_HELP_STRING.
Ok with that change.

thanks,
Tom