[Bug libstdc++/127424] 27_io testsuite: opening a FIFO with O_RDWR is undefined in POSIX; 9964.cc also stopped testing PR 9964 in 2004

[redi at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=127424

--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> ---
(In reply to Jonathan Wakely from comment #1)
> For completeness, should we restore the ios_base::trunc as well? Your patch
> doesn't do that.

Since it serves no purpose here, dropping it is fine.