x86: IB700 watchdog timer driver, run qemu with '-watchdog ib700'.

If the system enters the debugger, or otherwise hangs, the watchdog will automatically reboot the system.

Note: entering the debugger should stop the watchdog (so the debugger is usable without it being rebooted), but does not currently.
build, x86_64: output a 32-bit ELF binary on x86_64, which allows booting with unpatched GRUB.

This has required some changes to KernelElf to handle the fact that the kernel ELF is a 32-bit ELF object, and therefore addresses have been truncated.
Also, this has been done with a 32-bit assembly stub that enters long mode and then jumps to the normal 64-bit assembly entry point.
build: add elf32-i386 as an optional target for x86_64-pedigree binutils