gh-125022: add support for simple SIMD features detection

[picnixz]

In #124951, there has been some initial discussion on improving the performances of base64 and possibly {bytearray,bytes,str}.translate using SIMD instructions.

More generally, if we want to use specific SIMD instructions, it'd be good if we at least know whether we can use them or not. This PR is a PoC, experimental and (hence the skip news).

Note that the detection is essentially based on what was done in the blake2 module (though the flags being detected are different in this case but we can always add all those that are needed). To prepare for a harder detection of AVX instructions support, I added all the flags that are known to CPUID and possibly relevant. Note that more work needs to be done for a production use, especially in autoconf I think.

Note

The detection of a wider large family of CPUs (here we just assume Intel for simplicity and because we don't want to be overcomplicated for now) is still an ongoing work.

cc @gpshead

• Issue: Provide detection for SIMD features in autoconf and at runtime #125022

[rruuaanng]

I think the updated flag declaration is really good. It’s just for improving readability and not for public exposure, which is awesome.