argument in parentheses so these macros are safe to use and invocations
with an expression as the argument like __bswap32_const(42 << 23 | 13)
work as expected. Additionally, mask all the individually shifted bytes
as appropriate so the bytes which exceed the width of the respective
__bswapN_const() macro in invocations like __bswap16_const(0xdead600d)
are ignored like it's the case with the corresponding __bswapN_var()
function.
MFC after: 3 days
