Fix macro-not-found error with rust-nightly

[stefunctional]

Running cargo test fails complaining that the macro stringified_module_code cannot be found in this scope.

Version: rustc 1.80.0-nightly (e82c861d7 2024-05-04)

error: cannot find macro `stringified_module_code` in this scope
  --> src/libc.rs:9:10
   |
9  | #![doc = stringified_module_code!()]
   |          ^^^^^^^^^^^^^^^^^^^^^^^ consider moving the definition of `stringified_module_code` before this call
   |
note: a macro with the same name exists, but it appears later at here
  --> src/libc.rs:68:18
   |
68 |     macro_rules! stringified_module_code {() => (
   |                  ^^^^^^^^^^^^^^^^^^^^^^^

I am not sure because rules around macro scopes are somewhat complex, but it seems that the macro should not be found either with textual scope or path-based scope (none by default), so it looks like rustc fixed an implementation bug incorrectly allowing this macro to be found, but I could be wrong.

[stefunctional]

The CI failures seem unrelated to this PR -- some .NET issue.

[danielhenrymantilla]

Awesome thanks! I'll try to make a release out of this shortly 🙏