win32/setup.mak: rename RUBY_RELEASE_DATE
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@46394 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
win32/setup.mak: rename RUBY_RELEASE_DATE
RUBY_RELEASE_DATE, same as other platforms.
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@46394 b2dd03c8-39d4-4d8f-98ff-823fe69b080e