Check that soft packed unions can have members with different widths.
Check that the `soft` qualifier implies `packed` and that nested soft
packed unions use the same representation recursively.
Also check that member bits are right-justified and that assignments to
narrower members leave the MSBs beyond the member bits unchanged. Check
that soft packed unions reject default member values.
Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Lars-Peter Clausen