Exit on startup if SSE4.2 is not available

[190n]

Bun does not support x86_64 CPUs without SSE4.2 (older than Intel Nehalem or AMD Bulldozer) at this time, even in our x64-baseline builds. On unsupported CPUs, currently Bun crashes with "illegal instruction" at some unpredictable point depending on what you call. We should instead perform CPU feature detection as early as possible at startup, and call a function that prints an error message and exits if desired features are missing. This function should be in a separate object file so that we can compile it using minimal x86_64 features (so we don't use an illegal instruction while trying to print this error).

In non-baseline builds, we should check for AVX2 and crash with an error telling them to use the baseline build.

[190n]

For context, in terms of microarchitecture levels:

• All x86_64 CPUs are at least v1, supporting SSE and SSE2
• Bun x64-baseline requires some features in v2, such as SSE4.2 (specifically we target nehalem)
• Bun x64 requires features in v3, such as AVX2 (specifically we target haswell)
• The latest Intel CPUs support v3 for consumers and v4 for some servers (it's complicated...) while the latest AMD CPUs support v4. I believe the last CPUs to not support v3 are the Jasper Lake family from 2021. v4 will likely not be broadly available for a long time.
  • edit: there are Intel processors launched in 2023 that don't have AVX. Only embedded CPUs, though. Jasper Lake was the last consumer family to lack AVX, but it's still found in many Chromebooks.