* nm.c (numeric_forward): Treat undefined symbols as "less than" defined

* nm.c (numeric_forward): Treat undefined symbols as "less than" defined
symbols with zero values.  If numeric values are equal, or both symbols are
undefined, sort alphabetically.  Don't assume that the difference of two
bfd_vma values will truncate to "int" and still have the same sign.
(numeric_reverse): Call numeric_forward and negate the result.
(print_symbol_info_bsd): For undefined symbols, print leading spaces equivalent
to the width of a printed bfd_vma, rather than assuming that 8 will look right.