> I'm not sure if this patch is noteworthy on its own, but perhaps it was posted because it implies this CPU feature is now supported or soon to be supported by OpenBSD.

OpenBSD has supported mandatory BTI/IBT on Intel CPUs (11th Gen+) and arm64 (Apple M2) since 7.4 (Oct 16, 2023).

https://www.openbsd.org/innovations.html

"Mandatory enforcement of indirect branch targets (BTI on arm64, IBT on Intel amd64), unless a linker flag (-Wl,-z,nobtcfi) requests no enforcement."

https://marc.info/?l=openbsd-ports&m=168899645126958&w=2

OpenBSD recently disabled retpolines by default because they are incompatible with IBT, so there has been some work done recently that this patch could help with, e.g: adding missing indirect branch target instructions (endbr64), previously hidden by retpoline. OpenBSD has done a lot of work to push these changes into the entire software ecosystem.