[llvm] [flang-rt] Avoid duplicate definition of `std::__libcpp_verbose_abort` (PR #175551)

[Markus Mützel via llvm-commits]

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mmuetzel wrote:

> Our case is a bit special because ot must be the first #include, while for and it is sufficient to be treated like one header among others.

There might be exceptions to that. But for most projects that I've seen so far, there is a rule to include the `config.h` header before *any* other header in each translation unit.

Introducing such a `config.h` header with these rules feels like it could be a larger independent project to what I was attempting here. I agree that this would be better than the current "monkey patching" though.

Would it be ok to add a header named `stl-overrides.h` that would be included via `-include` or `/FI` on the command line in this PR? Making that a "proper" `config.h`-style header with the appropriate inclusion rules could be done in follow-up changes. (I'd prefer to leave the latter part to a contributor or maintainer who is a bit more familiar with the project and tools like `clang-tidy` than myself.)

Does that sound ok?

https://github.com/llvm/llvm-project/pull/175551