copyinargs: Replace a hand-written string copy loop with strlcpy(3).  Carefully
reuse return value of strlcpy(3) to iterate.
Implement and enable TOPDOWN_VM. From Chuck Silvers.
The sparc64 port switched to TOPDOWN_VM finally.
Other boot loaders name ELF *.sym, not *.syms.  Follow that convention.
copyinargs: Redo previous; if given fakearg is longer than arg buf (which is
very unlikely to happen), there's no point to continue with truncated arg.
Just give up and return E2BIG.
Remove -mc68000 asm option for GCC4.8 (or new binutils?).
With this option, new gcc complains that "boot_ustar.S:21: Error:
selected processor does not have all features of selected architecture".
I'm not sure about the essence of this error, but this option maybe
not needed because there is no need to consider about 68000 here.
Remove extraneous sysctl setup calls now done as part of regular attach.
Use ldscript.  Identical output confirmed.
Some architectures like SPARC need to apply a fixed offset to the return
address. Introduce such a constant.
Using bcopy/memcpy with NULL arguments is valid as long as the size is
also 0.