signal_catcher: print errno when tombstoned_notify_completion fails.

Failure here could either be someone internal closing our FD (EBADF) or
tombstoned closing its end of the socket (EPIPE). Print the error to
disambiguate the cases.

Bug: 67805174
Test: treehugger
Change-Id: Ie35cb31218b5bb08757e61360c6539d39eece08b
(cherry picked from commit ff9e43fa6dcd44cecb81149c8410c071ef840723)
1 file changed