kernel config file.
- Add WORLD_FLAGS and KERNEL_FLAGS so you can build world and kernel with
extra make options such as -jX to speed up release builds.
- When building kernels, allow their hints to tag along, and use this to
install hints onto the boot floppy. Since the boot floppy doesn't load
loader.4th, we have to change device.hints to strip comments and change
each line to an explicit set command.
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