Rollup merge of #98394 - Enselic:fixup-rustc_main-renames, r=petrochenkov

Fixup missing renames from `#[main]` to `#[rustc_main]`

In #84217 `#[main]` was removed and replaced with `#[rustc_main]`. In some places the rename was forgotten, which makes the current code confusing, because at first glance it seems that `#[main]` is still around. Perform the renames also in these places.

I noticed this (after first being confused by it) when working on #97802.

r? `@petrochenkov`

(since you reviewed the other PR)

compiler/rustc_ast/src/entry.rs

@@ -2,7 +2,7 @@
 pub enum EntryPointType {
     None,
     MainNamed,
-    MainAttr,
+    RustcMainAttr,
     Start,
     OtherMain, // Not an entry point, but some other function named main
 }