Change the interfaces of these functions to save space. The code
that takes the least amount of space is often the opposite to what
you might expect. E.g., it helps to waste a few bytes passing
pointers so that the compiler can't see that certain addresses
are identical (gcc likes to waste space by reloading fat constants
even when the constant is already in a register).
Rewrite getbootdev() to save 80 bytes of space and to make it less
ugly. 32 bytes were saved simply by omitting the continue statements
in the pseudo-switch.
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