There isn't anything specific about the target in these cases an in
general recipes should touch CFLAGS. This ensures people don't
copy/paste bad example usages. In reality, behaviour is mostly
unchanged.
(From OE-Core rev: ae6e7dd19b6da81090a38792dfdf31b459290466)
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>