`--update-checkfiles` generates double line breaks on Windows?

[mbovel]

While working an #23453 with @Jannyboy11 yesterday, it seemed testCompilation --update-checkfiles on his Windows machine generated checkfiles with double line breaks.

[Jannyboy11]

If this issue is still open by the next spree, I'd like to join again and work on this.

[som-snytt]

I expected the issue to be git config, but .gitattributes has *.check text eol=lf; one might assume that extraneous \r\r\n would eventually reduce to \n.

But the correct way to divide a string into lines is linesIterator or equivalent.

The other issue is that file paths were written in windows fashion.

Worth mentioning that these issues were addressed years ago in partest and it's always nicer to inherit solutions from the past.