machine-overrides-extender.bbclass: Postpone overrides processing
We need to keep a reference to the original MACHINEOVERRIDES value so
it can be reprocessed as need. This allow the compatibility with
existing BSP's while fixing the complex multilib interactions.
I'd like to record that Richard Purdie was key to solve this issue.
Its implications were beyond my understanding until he guided me and
provided a prototype fix.
Signed-off-by: Otavio Salvador <otavio@ossystems.com.br>
(cherry picked from commit
d227cc133101ecbce25fc4f775863107537f883d)
