`i686-unknown-freebsd` uses `base.cpu = "pentium4"` but the version in ports patches it to be `base.cpu = "pentiumpro"

[estebank]

https://github.com/freebsd/freebsd-ports/blob/2ed61cbd3997f268d71b7df2a27d026aabb76477/lang/rust/files/patch-compiler_rustc__target_src_spec_i686__unknown__freebsd.rs#L1C4-L11

They've been carrying this patch since 2017.

[emaste]

See https://reviews.freebsd.org/D47227