Restore 72845 with fn main

rust-lang/rust#72845 (comment)

Author: Alexendoo

fixed/72845.rs ices/72845.rs

@@ -43,3 +43,5 @@ impl<T: Spec1> Foo for T {
 impl<T: Spec2> Foo for T {
     fn Bar() {}
 }
+
+fn main() {}