cli: --perf-prof only works on Linux

--perf-prof-related flags have been removed in V8 on non-linux devices, and so we should note that in testing here as well as in docs.

See:

• https://chromium-review.googlesource.com/c/v8/v8/+/1993969
• https://chromium-review.googlesource.com/c/v8/v8/+/1993978

This broke in Electron, which is how i discovered it.

Checklist

• make -j4 test (UNIX), or vcbuild test (Windows) passes
• tests and/or benchmarks are included
• documentation is changed or added
• commit message follows commit guidelines