ruby/util.h: DECIMAL_SIZE_OF_BITS

* include/ruby/util.h (DECIMAL_SIZE_OF_BITS): a preprocessor
  constant macro to approximate decimal representation size of n-bits
  integer.
* iseq.c (register_label): use DECIMAL_SIZE_OF_BITS for better
  approximation.
* ext/bigdecimal/bigdecimal.c (BigMath_s_log): ditto.
* common.mk (iseq.o), ext/bigdecimal/depend (bigdecimal.o): add
  dependency to ruby/util.h for DECIMAL_SIZE_OF_BITS.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@44562 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
* 2014-01-12

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@44563 b2dd03c8-39d4-4d8f-98ff-823fe69b080e