fix-comments.py on windows

Stream: mathlib4

[Yury G. Kudryashov]

Today, I tried to run fix-comments.py on a Windows computer. There were two issues:

• [x] it tries to open files in the current locale which was not utf-8; fixed in !4#2761 (pending review)
• [ ] it writes the output with CRLF newlines; I tried to add newline='\n' to some opens this didn't fix the bug.

P.S.: Then I fix the bug for me by coming home to my linux computer.

[Eric Wieser]

I usually just configure git to discard crlf

[Yury G. Kudryashov]

git discards crlf but fix-comments.py shows one huge diff chunk.

[Eric Wieser]

Ah, then we should ask git to normalize the whitespace before prompting the user

[Eric Wieser]

Because we'll have the same problem if the user is using one of the other git crlf settings