Fix System V ABI for packed structs with misaligned fields #14324
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Fixes #9873. Section 3.2.3 of the System V ABI reference says: (emphasis own)
The same behavior is verified with C on Clang. Actually calling
Procs that take or return those misaligned structs will most likely require #14323 as well, asbyvalandsretare now mandatory.On an unrelated note: while the reference says "eight eightbytes", an earlier revision said "four" instead, which is what Crystal currently uses for classification. This probably won't matter unless Crystal supports 512-bit vectors natively.