coreutils: use single binary in symlink method

coreutils: use single binary in symlink method

The symlink method is faster, since there is no shell fork/exec, and
provides extra space savings.

Signed-off-by: Carlos Santos <casantos@datacom.ind.br>
[Thomas: use the symlinks method not only for the merged /usr case,
but also in the non-merged case to be consistent, and therefore adjust
the logic that was moving the shell wrappers to a logic that recreates
the symlinks.]
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>