internal.h to calculate required buffer size to pack integers.
  (rb_absint_numwords): Ditto.
  (rb_absint_singlebit_p): Ditto.
  [ruby-core:42813] [Feature #6065]



git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@42208 b2dd03c8-39d4-4d8f-98ff-823fe69b080e