https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113230
--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> --- The point of the test is to write out a byte that isn't valid UTF-8, and check that it's printed unchanged, as a single byte. If something does some kind of iconv-like conversion on the test output and "fixes" the non-UTF-8 output, then the test's assumption will not hold.
