[clang] [clang][CIR] Match CIR return value with OGCG using mem2reg (PR #227241)

[Chibuoyim Ogbonna via cfe-commits]

bruteforceboy wrote:

@banach-space, for [223963](https://github.com/llvm/llvm-project/issues/223963) I think we'll eventually need a standard set of `opt` passes for these tests.

Currently, [`addv.c`](https://github.com/bruteforceboy/llvm-project/blob/197c16add5b16f4bd68c4f4bae115723e74330e2/clang/test/CodeGen/AArch64/sve/addv.c#L3) and [`dup.c`](https://github.com/bruteforceboy/llvm-project/blob/main/clang/test/CodeGen/AArch64/sve/dup.c#L3) also run `instcombine` and `tailcallelim`. I left those out here because they turn `mul` into `shl`, which needs more check updates, and I wanted to get CI green quickly.

Another PR to align the `opt` pipelines can follow this.

https://github.com/llvm/llvm-project/pull/227241