Runtime dispatch for sse4.2 or without in crc32c

[MBkkt]

crc32c already contains runtime dispatch, but only if you compiles with sse4.2.
So if I want to compile x86_64 binary without sse42 it will be always slow, even if I run on modern cpu.
It's possible to have runtime dispatch between different architecture, you can see example in simdjson https://github.com/simdjson/simdjson/blob/master/HACKING.md#runtime-dispatching

So what do you think?

From another side probably most of users compiles with sse4.2 now

But it will be possible to try to improve things with avx, but without switching to avx for whole library
Not sure is it good or not, because switching between avx instructions and sse has significant runtime cost. Probably depends on input size