amd64/i386/pc98 endian.h with stubs.
In __bswap64_const(x) the conflict between 0xffUL and 0xffULL has been
resolved by reimplementing the macro in terms of __bswap32(x). As a side
effect __bswap64_var(x) is now implemented using two bswap instructions on
i386 and should be much faster. __bswap32_const(x) has been reimplemented
in terms of __bswap16(x) for consistency.
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