Handle prelude

I tried this code (minimized from core):

/* rustc requires these, gccrs doesn't currently
#![feature(no_core)]
#![feature(prelude_import)]
#![no_core]
*/

#[prelude_import]
pub use crate::prelude::*;

mod a {
    // Exports as `crate::assert`.
    #[macro_export]
    macro_rules! assert {
        () => {}
    }
}

mod prelude {
    pub use crate::assert;
}

mod other {
    assert!();
}

I expected to see this happen: Compiles
Instead, this happened:

<source>:101:5: error: unknown macro: [assert]
  101 |     assert!();
      |     ^~~~~~

For macros, this requires #1076 and #1576. Types/traits in the prelude also don't work, but don't appear to have any immediate blockers.

Meta

• What version of Rust GCC were you using, git sha if possible.
  gccrs (Compiler-Explorer-Build-gcc-c7b7e297ea4b688ef9fb51a8aee2a8b2af39ac1c-binutils-2.40) 13.0.1 20230417 (experimental)

Start with the minimized Rust reproduction in the issue and inspect how gccrs handles #[prelude_import], macro exports, and macro lookup. Review the related blockers #1076 and #1576 before changing scope. Done means the reproduction compiles with the prelude macro available, while checking whether type and trait prelude cases also need coverage.