[llvm] [RISCV] Disable generic DAG combines at -O0 to preserve debuggability (PR #219082)

[Craig Topper via llvm-commits]

topperc wrote:

Doesn't this mean invalid immediate shift amounts won't get canonicalized. Or ANDing with all ones won't be removed. I think there might be some code in RISCVISelDAGToDAG.cpp for selecting shift+and that assume these things happened. 

https://github.com/llvm/llvm-project/pull/219082