This (almost) gives us the address space back (at the bottom) that we lost
at the top.
Region 0 has traditionally been reserved for IA-32 emulation, which has not
been of great interest. By starting 64-bit processes at the 4G boundary we
at least preserve some of the advantages:
1. Any invalid pointer cast (from int to pointer and back) will still
always fail and not only when more than 4GB of memory is in use.
2. Memory sharing between 64-bit and 32-bit processes is still possibly
by using addresses < 4G.
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 two may be different (ie, build vs. runtime))
Allow ldscript's SEARCH_DIR do be rooted somewhere other than `/'.
(in this case at TOOLS_PREFIX)
These changes are most helpful during `make buildworld' so that the shared
libs built in the middle of `make buildworld' are used vs. the ones in
/usr/lib on the build machine.
Submitted by: ru
