* rb_w32_fstat{,i64}: speed up.  adjuting timestamps in this function
  is to get rid of the side effect of ENV["TZ"].  then, if ENV["TZ"] is
  not set, no need to adjust.  this change makes File#stat about 60%
  faster.


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@48394 b2dd03c8-39d4-4d8f-98ff-823fe69b080e