use ifchange tool for rb_mjit_header.h
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@62194 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
use ifchange tool for rb_mjit_header.h
tool. cmp command is not available on Windows.
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@62194 b2dd03c8-39d4-4d8f-98ff-823fe69b080e