bitbake.conf: Whitelist MACHINE variable in PACKAGE_ARCHS
PACKAGE_ARCHS represents all compatible architectures for a given machine.
It makes no sense for this variable to change any task checksums as it doesn't
inject any machine dependency into any known task. Multimachine means machine
specific packages will be detected through other variables.
Before this patch, even native packaging tasks were ending up being marked as
machine specific.
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
