Using `-fvisibility=hidden` when building the kernel, and then
`--discard-all` when stripping it, we shave almost 100KiB off of the
resulting ELF file.
Also dropped some unused symbols from the linker script, and rearranged
the sections so that the file is able to be mapped directly into memory
instead of having each section copied.
Eventually the UEFI headers should be brought in from their own project,
but for now, like the other projects under external/, these are being
copied into this repository.
Tags: boot uefi
