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).
The target machine is represented by TARGET_ARCH. MACHINE_ARCH always
represents the host machine. When TARGET_ARCH is not defined, it is
assumed to be equal to MACHINE_ARCH. This means that we're building a
native toolset by default. We're creating cross-compilation tools when
MACHINE_ARCH != TARGET_ARCH.
TARGET_ARCH is defined when building binutils as part of the bootstrap
build and is set to reflect the architecture we're currently cross-
building. With this change binutils is ready for cross-building.