tuklib_integer: Improve unaligned memory access.

Now memcpy() or GNU C packed structs for unaligned access instead
of type punning. See the comment in this commit for details.

Avoiding type punning with unaligned access is needed to
silence gcc -fsanitize=undefined.

New functions: unaliged_readXXne and unaligned_writeXXne where
XX is 16, 32, or 64.
1 file changed