[clang] [clang] Introduce __builtin_splatvector (PR #212758)

[Paul Osmialowski via cfe-commits]

pawosm-arm wrote:

> > > Is there even a platform-generic type for scalable vectors yet?
> > 
> > 
> > Sadly, no.
> 
> That seems like the thing we should solve first. After that I wouldn't be surprised if we didn't need this builtin at all.

No, it's the other way round. When I tried to introduce a generic vector type, one of the comments was we should first improve builtin coverage of the sizeless vector types...

https://github.com/llvm/llvm-project/pull/212758