[Bug preprocessor/65852] Incorrect escaping in depfiles

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65852

--- Comment #7 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Hmm, I thought \ would be converted into / by the time we reach here for
windows.  I wonder if that is the better fix.