Remove libkern, leave just header.
Boot stuff dependencies from NetBSD.
Patch by Antoine Leca. Relocated to src/sys.
The port is using the same libminc.a as usual MINIX services (and does
not use NetBSD libkern); the headers imported from NetBSD sys/ tree
have been kept to a minimum (still numbers higher than 30 though.)
Note the peculiar way to use libraries (libsa, libi386, etc.): the
source code is shared, but each component builds its own copy of the
library, with its own set of preprocessor defines.