[llvm] [CodeGen] Allow larger number of operands to be compiled by SelectionDAG (PR #122737)

[Nikolay Panchenko via llvm-commits]

npanchen wrote:

> I think that vector types this large should be rejected in the frontend.

Are you suggesting to restrict vector size (in elements) to 2^16-1 ? At least now clang [allows 2^31](https://github.com/llvm/llvm-project/blob/main/clang/lib/Sema/SemaType.cpp#L2383)  (in elements)  that matches what GCC can handle too. 

https://github.com/llvm/llvm-project/pull/122737