wait6(): fix reporting of orphan exits

[kib]

Summary

Due to the way the exit from the loop checking for orphans was
organized, the status of an eligible orphan was dropped to the floor.
Directly exit from kern_wait6() if orphan to be reported.

exit1() did not woke up the real parent, only the debugger and procdesc
waiter.  Look up the real parent and wake it up on the orphaned child
exit.

Mark the process which was reported through the orphaned list with a
flag, to avoid duplicate wait() returns.  This is needed because the
process itself does not manage its orphans list, an orphan is kept there
until reparented.

[kib]

Will be consumed by D58264