This PR updates the lint added in 9b40bd7 to ignore repr(C) structs that also
have repr(packed) or repr(align(n)).
As these representations can be modifiers on repr(C), it is assumed that users
that add these should know what they are doing, and thus the the lint should not
warn on the respective structs. For example, for the time being, using
repr(packed) and manually padding a repr(C) struct can be done to correctly
align struct members on AIX.
