Rollup merge of rust-lang#94308 - tmiasko:normalize-main-ret-ty, r=oli-obk

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]
```

Author: Manishearth

compiler/rustc_codegen_cranelift/src/main_shim.rs

@@ -51,7 +51,10 @@ pub(crate) fn maybe_create_entry_wrapper(
         // late-bound regions, since late-bound
         // regions must appear in the argument
         // listing.
-        let main_ret_ty = tcx.erase_regions(main_ret_ty.no_bound_vars().unwrap());
+        let main_ret_ty = tcx.normalize_erasing_regions(
+            ty::ParamEnv::reveal_all(),
+            main_ret_ty.no_bound_vars().unwrap(),
+        );
 
         let cmain_sig = Signature {
             params: vec![

compiler/rustc_codegen_ssa/src/base.rs

@@ -407,7 +407,10 @@ pub fn maybe_create_entry_wrapper<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
         // late-bound regions, since late-bound
         // regions must appear in the argument
         // listing.
-        let main_ret_ty = cx.tcx().erase_regions(main_ret_ty.no_bound_vars().unwrap());
+        let main_ret_ty = cx.tcx().normalize_erasing_regions(
+            ty::ParamEnv::reveal_all(),
+            main_ret_ty.no_bound_vars().unwrap(),
+        );
 
         let Some(llfn) = cx.declare_c_main(llfty) else {
             // FIXME: We should be smart and show a better diagnostic here.

compiler/rustc_monomorphize/src/collector.rs

@@ -1270,7 +1270,10 @@ impl<'v> RootCollector<'_, 'v> {
         // late-bound regions, since late-bound
         // regions must appear in the argument
         // listing.
-        let main_ret_ty = self.tcx.erase_regions(main_ret_ty.no_bound_vars().unwrap());
+        let main_ret_ty = self.tcx.normalize_erasing_regions(
+            ty::ParamEnv::reveal_all(),
+            main_ret_ty.no_bound_vars().unwrap(),
+        );
 
         let start_instance = Instance::resolve(
             self.tcx,