Add FileCheck for build_correct_coerce

Author: eval-exec

tests/mir-opt/build_correct_coerce.rs

@@ -1,5 +1,3 @@
-//@ skip-filecheck
-
 // Validate that we record the target for the `as` coercion as `for<'a> fn(&'a (), &'a ())`,
 // and not `for<'a, 'b>(&'a (), &'b ())`. We previously did the latter due to a bug in
 // the code that records adjustments in HIR typeck.
@@ -8,5 +6,8 @@ fn foo<'a, 'b>(_: &'a (), _: &'b ()) {}
 
 // EMIT_MIR build_correct_coerce.main.built.after.mir
 fn main() {
+    // CHECK-LABEL: fn main(
+    // CHECK: let _1: for<'a> fn(&'a (), &'a ());
+    // CHECK: _1 = foo as for<'a> fn(&'a (), &'a ())
     let x = foo as for<'a> fn(&'a (), &'a ());
 }