When invoking pmbootstrap build most packages default to the host arch,
however depending on your workflow it might be preferrable to default to
the device arch.
Add a new config option "build_default_device_arch" which when set will
make "pmbootstrap build" prioritise the device arch over the native
arch.
Default to False to preserve the old behaviour and don't ask during
pmbootstrap init as this may not be relevant for most folks.
Reviewed-by: Oliver Smith <ollieparanoid@postmarketos.org>
Co-developed-by: Oliver Smith <ollieparanoid@postmarketos.org>
Link: https://lists.sr.ht/~postmarketos/pmbootstrap-devel/%3C20230418-build-default-arch-v5-2-5223fab65867@postmarketos.org%3E
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