util: avoid referencing `time.clock()` on Windows when missing (
issue6238)
It's been removed in 3.8, and issues a deprecation warning since 3.3.
Differential Revision: https://phab.mercurial-scm.org/D7780
To run the tests, do:
cd tests/
python run-tests.py
See https://mercurial-scm.org/wiki/WritingTests for
more information on writing tests.