Cannot build on aarch64 (Apple Silicon Chips)

[Willian Z]

weld/python/grizzly/grizzly/common.h

Line 4 in dcbba9a

 #include <immintrin.h> 

not available on non-x86 archs, will cause build err

FYI: example fix:
https://github.com/suijingfeng/vkQuake3/blob/master/code/SDL2/include/SDL_cpuinfo.h#L85