n method.  Is there a better way?
     Maybe variable-length arrays per notes below.
<li> Alpha Unicos 21164, 21264: <code>.align</code> is not used since it pads
     with garbage.  Does the code get the intended slotting required for the
     claimed speeds?  <code>.align</code> at the start of a function would
     presumably be safe no matter how it pads.
<li> ARM V5: <code>count_leading_zeros</code> can use the <code>clz</code>
     instruction.  For GCC 3.4 and up, do this via <code>__builtin_clzl</co