787c6f3365
Normalize main return type during mono item collection & codegen
The issue can be observed with `-Zprint-mono-items=lazy` in:
```rust
#![feature(termination_trait_lib)]
fn main() -> impl std::process::Termination { }
```
```
BEFORE: MONO_ITEM fn std::rt::lang_start::<impl std::process::Termination> ````@@```` t.93933fa2-cgu.2[External]
AFTER: MONO_ITEM fn std::rt::lang_start::<()> ````@@```` t.df56e625-cgu.1[External]
```
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| .. | ||
| src | ||
| Cargo.toml | ||
| README.md | ||
Please read the rustc-dev-guide chapter on Backend Agnostic Codegen.