[llvm] [RISCV] Recognize VLA shift pairs from shuffle masks (PR #127710)

[Philip Reames via llvm-commits]

preames wrote:

> is there some special C++ case on that I'm unaware of?

For once, google's AI was useful when I tried to search this question.  Apparently in c++17, there are cornercases with reference capture of structural bindings which disappear in c++20.  I'm going to add these explicitly as value captures to avoid the error on the strict c++17 bots.  

https://github.com/llvm/llvm-project/pull/127710