qtestcase/Unix: remove fprintf from signal handler

It's not async-signal-safe, so don't use it. Instead, let's use writev()
(which should write atomically and we won't need to have a buffer) and
std::to_chars to format numbers where available (where not, we roll out
our own implementation with divisions).

Pick-to: 6.3
Change-Id: I5ff8e16fcdcb4ffd9ab6fffd16eb70a158f44864
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>

0 files changed, 0 insertions, 0 deletions