Emit a single privacy error for multiple fields on the same struct expression

Collect all unreachable fields in a single struct literal struct and emit a single error, instead of one error per private field.

```
error[E0451]: fields `beta` and `gamma` of struct `Alpha` are private
  --> $DIR/visibility.rs:18:13
   |
LL |     let _x = Alpha {
   |              ----- in this type
LL |         beta: 0,
   |         ^^^^^^^ private field
LL |         ..
   |         ^^ field `gamma` is private
```

1 files changed, 18 insertions, 5 deletions

diff --git a/tests/ui/structs/default-field-values/visibility.rs b/tests/ui/structs/default-field-values/visibility.rs
index e1f76a5fe24..ff1245551b0 100644
--- a/tests/ui/structs/default-field-values/visibility.rs
+++ b/tests/ui/structs/default-field-values/visibility.rs
@@ -1,5 +1,6 @@
 #![feature(default_field_values)]
 pub mod foo {
+    #[derive(Default)]
     pub struct Alpha {
         beta: u8 = 42,
         gamma: bool = true,
@@ -7,10 +8,22 @@ pub mod foo {
 }
 
 mod bar {
+    use crate::foo::Alpha;
     fn baz() {
-        let x = crate::foo::Alpha { .. };
-        //~^ ERROR field `beta` of struct `Alpha` is private
-        //~| ERROR field `gamma` of struct `Alpha` is private
+        let _x = Alpha { .. };
+        //~^ ERROR fields `beta` and `gamma` of struct `Alpha` are private
+        let _x = Alpha {
+            beta: 0, //~ ERROR fields `beta` and `gamma` of struct `Alpha` are private
+            gamma: false,
+        };
+        let _x = Alpha {
+            beta: 0, //~ ERROR fields `beta` and `gamma` of struct `Alpha` are private
+            ..
+        };
+        let _x = Alpha { beta: 0, .. };
+        //~^ ERROR fields `beta` and `gamma` of struct `Alpha` are private
+        let _x = Alpha { beta: 0, ..Default::default() };
+        //~^ ERROR fields `beta` and `gamma` of struct `Alpha` are private
     }
 }
 
@@ -20,10 +33,10 @@ pub mod baz {
     }
 }
 fn main() {
-    let a = baz::S {
+    let _a = baz::S {
         .. //~ ERROR field `x` of struct `S` is private
     };
-    let b = baz::S {
+    let _b = baz::S {
         x: 0, //~ ERROR field `x` of struct `S` is private
     };
 }