If we detected that the OS supports a version of system forkfd (Linux
pidfd, FreeBSD procdesc), the forkfd_wait() function was using only the
system waiting implementation, which of course can't work for file
descriptors created with FFD_USE_FORK. So just detect EBADF and attempt
again.
If the file descriptor is neither one of our pipes nor a system forkfd,
bad things will happen...
Fixes: QTBUG-82351
Change-Id: I4e559af2a9a1455ab770fffd15f59fb3160b22eb
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@gmx.de>
ba5e2ce49a