clippy: actually fail if there are any warnings
So far, only errors would trip the CI, this makes it so all warnings are
elevated to errors, making it a CI fail if any warnings are present.
This was the intended behavior, I just missed this when adding clippy.
@echo off
rem Double-click this file to (re)build Mercurial for Windows in place.
rem Useful for testing and development.
cd ..\..
del /Q mercurial\*.pyd
del /Q mercurial\*.pyc
rmdir /Q /S mercurial\locale
python setup.py build_py -c -d . build_ext -i build_mo
pause