[Bug libstdc++/79820] std::ifstream sets errno to zero

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79820

--- Comment #3 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Comment on attachment 40966
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=40966
patch

It's quite possible that "errno" is a macro for something called "__errno" on
some systems, so this would fail to compile. I suggest something like
__save_errno instead, and it also needs to be done on line 275.