procutil: import concerns about creationflags on Windows from D1701...
procutil: import concerns about creationflags on Windows from D1701
I don't have the need anymore for the change in D1701 nor the time to
investigate the changes on all supported Windows platforms.
I import the stuff I learned on D1701 in the `runbgcommand` so the next people
working on it can starts from there.
Differential Revision:
https://phab.mercurial-scm.org/D5229