_BitInt: Update alignment of _BitInt(N) for N > 64
For N > 64, _BitInt(N) is aligned to 64 bits. Change
_BitInt(N) types are byte-aligned to the next greatest power-of-2 up to 64 bits.
to
_BitInt(N) types are byte-aligned to 64 bits.
For N > 64, _BitInt(N) is aligned to 64 bits. Change
_BitInt(N) types are byte-aligned to the next greatest power-of-2 up to 64 bits.
to
_BitInt(N) types are byte-aligned to 64 bits.