* ext/fiddle/extconf.rb: remove ffitarget.h generated by configure on
  mswin, because it's not normal file (cygwin's symlink) and have
  system attribute.


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@48954 b2dd03c8-39d4-4d8f-98ff-823fe69b080e