architecture-dependent and is needed by the ELF code.

defined in vsprintf.h.  (This may change, since vsprintf.h is a
non-standard name, but for now it's the one to use.)

There should be no need to include vsprintf.h just for DBG() statements,
since include/compiler.h forces it in for a debug build anyway.

Change semantics; relocate() now just finds a suitable location; it
doesn't actually perform the relocation itself.  Code in libprefix does
the copy in flat real mode.

advantage of the fact that we have to have a permanently-resident block
in base memory.

Note that we can't make real-mode calls immediately after relocate_to().

Preserves alignment requested via _max_align parameter to linker.

logic (e.g. avoiding memory regions with A20=0).