[Bug target/95732] Use CPU dispatching to support mixing -fcf-protection with -mindirect-branch and -mfunction-return

[josephcsible at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95732

--- Comment #1 from Joseph C. Sible <josephcsible at gmail dot com> ---
Thinking about this a bit more, it's a win for performance even if we ignore
CET completely. In particular, it would let a single binary use retpolines only
on CPUs that have the Spectre vulnerabilities that they mitigate.