[llvm] [LLVM][LangRef] Remove "n > 0" restriction from get.active.lanes.mask. (PR #152140)

[Sjoerd Meijer via llvm-commits]

sjoerdmeijer wrote:

> Don't we need to be able to convert this to back into an equivalent icmp ule and we need to perform a minus one during the reconstruction? So, with a zero value input we wrap to UINT_MAX?

This is probably it, I think this is most plausible explanation. 

https://github.com/llvm/llvm-project/pull/152140