count-leading-zeros: port to MSC; support types wider than 64 bits

count-leading-zeros: port to MSC; support types wider than 64 bits

The ideas behind the MSC port are stolen from Emacs.
* lib/count-leading-zeros.h:
Don't include verify.h: it's no longer needed, as types wider than
64 bits are now supported.
(COUNT_LEADING_ZEROS): New arg MSC_BUILTIN, for better
performance with MSC.  All uses changed.  Do not assume that TYPE
has at most 64 bits.
(count_leading_zeros_32): Assume 0 < X < 2**32, for speed.
All uses changed.  Fold the subtraction from 31 into the table.