* lib/stdbit.c (__gl_stdbit_clztab):
* lib/stdbit.in.h (__gl_stdbit_clzll):
[!_GL_STDBIT_HAS_BUILTIN_CLZ && !_MSC_VER]: Rewrite to avoid the
need for a lookup table in memory, and remove the lookup table.
Do this by shrinking the table to 64 bits and puttiung in a 64-bit
constant. Although this needs another round of shifts, it avoids
the need for a multiplication and memory access a la de Bruijn,
and is probably a win.