fix build for _KERNEL

Put missing END() markers to set ELF symbol size.

branches: 1.3.12; 1.3.24;
Remove some long dependant instruction sequences (ie allow parallel code).
Since 'rep stos' will have a long setup time, avoid doing it more than once.
For misaligned (start address or length) write an unaligned word at both
ends of the buffer then aligned 'rep stosd' the middle.
Use the same code for bzero().
bzero.S is left being compiled for a while (empty) - to avoid issues with
duplicate symbols in libc.a after update builds.

Don't unconditionally clear the direction flag. The ABI says it must always
be clear when making a function call, and 'cld' takes about 50 clock cyles
on the P4.

branches: 1.1.18;
Merge libkern + libc common files. As requested by core.

sync with HEAD

Rebase.

Rebase to HEAD as of a few days ago.