[llvm] [llvm-diff] add optional call to IRNormalizer (PR #123314)

[Serval MARTINOT-LAGARDE via llvm-commits]

Serval6 wrote:

Here is a version that allows you to launch the `llvm::IRNormalizer` directly from `llvm-diff`, thanks to the `--enable-ir-normalizer` flag.

https://github.com/llvm/llvm-project/pull/123314