* bignum.c (nlz16): Use __builtin_clz if possible.
  (nlz32): Use __builtin_clz or __builtin_clzl if possible.
  (nlz64): Use __builtin_clzl or __builtin_clzll if possible.
  (nlz128): Use __builtin_clzll if possible.

* configure.in: Check __builtin_clz, __builtin_clzl and
  __builtin_clzll.



git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@41976 b2dd03c8-39d4-4d8f-98ff-823fe69b080e