I wonder if the same is true for OpenBSD systems, given their greater focus on security.
But it definitely wasn't zero
The kernel itself should hopefully be unaffected by these issues though.
$ cc -v
OpenBSD clang version 10.0.1
Target: amd64-unknown-openbsd6.8
Thread model: posix
InstalledDir: /usr/bin
Threading is plenty fast, and the kernel has, like everything, bugs.