[clang] [clang][modules] Fix CodeGen options that can affect the AST. (PR #78816)

[Juergen Ributzka via cfe-commits]

ributzka wrote:

> LGTM, although are we sure none of the other options should be affecting? I just did a quick search and it seems like this is it.
> 
> I don't think it matters here, but the actual option that controls the macro is on `LangOptions` and where it's set has a "FIXME: Eliminate this dependency" where it directly parses the command line. As long as we're not changing the value the `LangOptions` version should always match.

I checked every usage of all codegen options when I did the original change, but I missed the double parsing of the command line argument in `LangOpts`. That was not a pattern I was looking for.

https://github.com/llvm/llvm-project/pull/78816