tests/test-gendoc-zh_CN.t

windows: use cpu-intensive task instead of real time in test

Windows profiling breaks when using real time instead of cpu, but we need the
extension function to show up, so make it do something instead of waiting.
I've also duplicated the test cases so that explicit real and CPU times are
tested (on platforms other than Windows)

Differential Revision: https://phab.mercurial-scm.org/D11003

#require docutils gettext

  $ $TESTDIR/check-gendoc zh_CN
  checking for parse errors