👍 fanquake approved a pull request: "build: Drop redundant `sys/sysctl.h` header check"
(https://github.com/bitcoin/bitcoin/pull/30327#pullrequestreview-2142044015)
ACK c0b5ea5901d0ed005bca345e5b2de8a502f6af75 - we could got the other way, and add nested #defs, but that doesn't seem worthwhile.