Merge #10057: [init] Deduplicated sigaction() boilerplate

Summary:
81a3857 Deduplicated sigaction() boilerplate (Thomas Snider)

Tree-SHA512: 705b73f285a3d76504ba01476e072fdce67731b65f309bb04e4bbd765556c37e127cb769b475de2d68b33f50d7737fb136aefa0fa7c725a11ad16a47b9d0365f

Backport Core PR 10057
https://github.com/bitcoin/bitcoin/pull/10057/files

Test Plan:

make check
bitcoind --testnet
ps aux | grep bitcoind
kill -s TERM <bitcoind-pid>
# bitcoind should be killed

bitcoind --testnet
rm ~/.bitcoin/testnet3/debug.log
ps aux | grep bitcoind
kill -s HUP <bitcoind-pid>
# debug.log should be recreated

Reviewers: deadalnix, Fabien, #bitcoin_abc

Reviewed By: Fabien, #bitcoin_abc

Differential Revision: https://reviews.bitcoinabc.org/D2961