[llvm] [NVPTX] Disable incorrect peephole optimizations (PR #79920)

[Justin Fargnoli via llvm-commits]

justinfargnoli wrote:

TLDR: I won't have the bandwidth to fix this in the foreseeable future. 

I implemented the fix that you suggested (and I agree that it's likely the right way to go). However, it wasn't trivial to fix the unit tests. That gave me pause about submitting a fix that I don't fully understand. e.g. I haven't run tests to assess the performance impact of the fix and I don't understand the original rationale for the change. So, instead of doing a deep dive on the fix, I'd like to remove the erroneous code for the time being and revisit it when necessary.  

https://github.com/llvm/llvm-project/pull/79920