[clang] [Preprocessor] Do not expand macros if the input is already preprocessed (PR #137665)

[Juan Manuel Martinez Caamaño via cfe-commits]

jmmartinez wrote:

> module maps don't get preprocessed, so I don't think it matters what that is set to. For normal module.modulemap files `Preprocessed` is `false`. I think it's fine to remove the true and see if anything breaks, the preprocessor just skips over that section anyway.

Currently a single test breaks: `Modules/initializers.cpp` which has preprocessor directives in the module source.

I guess then that this is an issue with the test. I'll try to propose a fix to the test then.

https://github.com/llvm/llvm-project/pull/137665