CTest normally terminates test processes on timeout using `SIGKILL`.
Offer tests a chance to exit gracefully, on platforms supporting POSIX
signals, by setting `TIMEOUT_SIGNAL_{NAME,GRACE_PERIOD}` properties.
Fixes: #17288
Since commit d1976cd1f2 (CTest: Fix timeout when grandchild keeps pipes
open, 2020-01-13, v3.17.0-rc1~169^2) we no longer hang, but the test
duration we report after the timeout is the amount of time the immediate
child ran before exiting. Fix the logic to instead report the actual
amount of time we spent monitoring the test before the timeout.
Fixes: #20509
When a test's process creates its own child and exits, the grandchild
may keep pipes open. Fix CTest logic to correctly timeout if the
grandchild does not exit and close the pipes before the timeout expires.
This was broken by commit b5e21d7d2e (CTest: Re-implement test process
handling using libuv, 2017-12-10, v3.11.0-rc1~117^2) which added an
unnecessary condition to the timeout handling.
Fixes: #20116
