add test for symbol visibility of `#[naked]` functions
tracking issue: #90957
This test is extracted from https://github.com/rust-lang/rust/pull/128004
That PR attempts to generated naked functions as an extern function declaration, combined with a global asm block that provides the implementation for that declaration.
In order to link declaration and definition together, some flavor of external linking must be used: LLVM will error for other linkage types. Specifically the allowed options are `#[linkage = "external"]` and `#[linkage = "extern_weak"]`. That is kind of an implementation detail though: to the user, a naked function should just behave like a normal function.
Hence it should be visible to the linker under the same circumstances as a normal, vanilla function and have the same attributes (Weak, External). Getting this behavior right will require some care, so I think it's a good idea to lock it in now, before making any changes, to make sure we don't regress.
Are there any interesting cases that I missed here? E.g. is checking on different architectures worth it? I don't think the other binary types (rlib etc) are relevant here, but may be missing something.
r? ``@bjorn3``
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