Makefile.in: suppress warnings

* Makefile.in (enc/jis/props.h): suppress `pointer-to-int-cast`
  warnings by using `offsetof`.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@46052 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
* 2014-05-23

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@46053 b2dd03c8-39d4-4d8f-98ff-823fe69b080e