Re-enable BF16 on x86 in debug builds with Clang 22 or later

[johnplatts]

There is a recent fix in LLVM 22 that fixes the bug with _BFloat16 in debug builds on x86, and this bug was fixed in LLVM pull request llvm/llvm-project#164565 (which has been recently merged into the LLVM trunk).

It is now safe to define HWY_SSE2_HAVE_SCALAR_BF16_TYPE to 1 in debug builds with Clang 22 and later on x86 with the fix in llvm/llvm-project#164565.

[jan-wassenberg]

How about we make the check >= 2300? The issue is that all the various pre-release LLVM versions already call themselves "22", but they might be before or after the fix. Or can we see more with HWY_COMPILER_CLANG3?

[stefson]

@johnplatts do you think you can ask upstream llvm for a backport to llvm-21 branch? I could do that as well, but you might be better at explaining them why this would be a good candidate (:

[johnplatts]

How about we make the check >= 2300? The issue is that all the various pre-release LLVM versions already call themselves "22", but they might be before or after the fix. Or can we see more with HWY_COMPILER_CLANG3?

A better alternative is HWY_COMPILER3_CLANG >= 220101 as Clang 22.1.1 is guaranteed to have the required fixes. I have updated this pull request to check for HWY_COMPILER3_CLANG >= 220101.

[jan-wassenberg]

Sounds good, thanks for updating.