sing, or would like to use,
     <code>mpn_umul_ppmm</code>, and the corresponding umul.asm file could be
     included in libgmp only in that case, the same as is effectively done for
     <code>__clz_tab</code>.  Likewise udiv.asm and perhaps cntlz.asm.  This
     would only be a very small space saving, so perhaps not worth the
     complexity.
<li> longlong.h could be built at configure time by concatenating or
     #including fragments from each directory in the mpn path.  This would
     select CPU sp