Currently its near impossible for other classes to sanely override
this value with their own default. By setting a weak default we can
allow other classes to change the default and allow end recipes to
again override this.
As far as I can tell, there shouldn't be any regressions from this
change.
(From OE-Core rev: 12b2a73d336d66596939eae5c9947d4054c0316e)
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>