configure: Make -Waddress-of-packed-member warnings be errors

configure: Make -Waddress-of-packed-member warnings be errors

We have now managed to eradicate all the places in the codebase
that triggered clang's -Waddress-of-packed-member warning. Remove
the compiler flag that exempted it from our usual -Werror policy.
This will prevent any new problematic code being added in future.

Signed-off-by: Peter Maydell <[email protected]>
Reviewed-by: Thomas Huth <[email protected]>
Reviewed-by: Philippe Mathieu-Daudé <[email protected]>
Message-Id: <20190208132112[email protected]>
Signed-off-by: Laurent Vivier <[email protected]>