... the following timeout failure.
http://rubyci.s3.amazonaws.com/rhel_zlinux/ruby-master/log/20210408T213303Z.fail.html.gz
```
[ 8871/21204] TestGCCompact#test_ast_compactstimeout: output interval exceeds 600.0 seconds.
timeout: the process group 28416 is alive.
PSOUT PGID PID ELAPSED %CPU VSZ COMMAND COMMAND
PSOUT 28416 28416 12:46 0.0 108120 gmake gmake TESTS=--hide-skip -v RUBYOPT=-w test-all
PSOUT 28416 28423 12:46 88.2 1446124 ruby ./test/runner.rb: TestGCCompact#test_ast_compacts
timeout: INT signal sent.
timeout: INT signal sent.
timeout: TERM signal sent.
timeout: TERM signal sent.
timeout: KILL signal sent.
```
This error repeatedly occurs on RHEL s390x.
This change sends SEGV when timeout occurs so that it should dump the backtrace.