[llvm] Use DIExpression::foldConstantMath() at the result of an appendOpsToArg() (PR #71721)

[Shubham Sandeep Rastogi via llvm-commits]

rastogishubham wrote:

@jmorse @adrian-prantl patch has been updated, I am unsure about what to do for DebugInfo/salvage-limit-expr-size.ll, because of this patch, there is no longer a limit of 128 salvageable instructions, because they get folded down to one instruction

https://github.com/llvm/llvm-project/pull/71721