packagegroup-*: set PACKAGE_ARCH before packagegroup inherit
The required order was changed in OE-Core commit:
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| allarch: Add warning about packagegroup
|
| Since we want to start including this class conditionally, detect cases
| where packagegroup files use the old ordering and inform the user they
| need to update this.
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Change-Id: If76ae87fadd4310ae0d1ae344a565683d4b34f9f Signed-off-by: Otavio Salvador <otavio@ossystems.com.br>
