This includes removing all vestiges of the old not-really supported
ability to build cross tools targeting non-FreeBSD systems, such as
m68k Lynx and NetBSD. Move as much duplicated code from platform
Makefiles into the shared Makefiles. Add a simple mechanism for
specifying ELF 'ldscripts'. Also share as many .h files as possible
(now a single bfd.h vs. one per platform).