It's as arch-specific as they come.

Doesn't really affect anything, but it is cleaner.

This lets use _attribute__((init_priority)) to control static constructor
order, useful for configuring interdependent global services.

Previously, the boot code assumed (by omission) that memory is initialized
to zero.  Apparently that is not the case, and this caused memory to become
corrupted.

Initialize .bss to zero to fix.

Not strictly needed, but better to know exacly where things end up.

We need the headers so we can provide the symbols to loaded libraries.
This means we cannot use objcopy to munge the binary format to elf32-i386,
as the loader doesn't understand this format.

Instead, add a separate 32-bit only stage (in elf32-i386 format) that loads
the 64-bit image into memory as its payload.  This keeps multiboot happy and
leave our headers alone.

Change the starting program counter to 0x201000 instead of 0; this allows the
ELF header to be present in the loaded image, and used for linking.

0x20000 will overflow into the 640k hole

Set up 32-bit entry point via linker script.