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: c127bb3a9b7b1d2ab2c833ff73186b6ead0dc29c)
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>