Clean up some horrible old code and drop usage of the old style *COMMAND
variable and MKTEMPDIRCMD whilst in here. This means we don't need to touch
OVERRIDES either.
(Bitbake rev: 6b79789769da160d0e7fca0f9c6044dc1e11a107)
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>