Rebase. Fix mutable iteration nit.

Author: Jonathan Turner

src/librustc_errors/emitter.rs

@@ -465,7 +465,7 @@ impl EmitterWriter {
                                     span: &mut MultiSpan,
                                     children: &mut Vec<SubDiagnostic>) {
         let mut spans_updated = self.fix_multispan_in_std_macros(span);
-        for child in &mut children.iter_mut() {
+        for child in children.iter_mut() {
             spans_updated |= self.fix_multispan_in_std_macros(&mut child.span);
         }
         if spans_updated {

src/test/ui/mismatched_types/issue-26480.stderr

@@ -4,7 +4,7 @@ error[E0308]: mismatched types
 26 |                   $arr.len() * size_of($arr[0]));
    |                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected u64, found usize
 ...
-38 |     write!(hello);
+37 |     write!(hello);
    |     -------------- in this macro invocation
 
 error: non-scalar cast: `{integer}` as `()`
@@ -13,7 +13,7 @@ error: non-scalar cast: `{integer}` as `()`
 32 |     ($x:expr) => ($x as ())
    |                   ^^^^^^^^
 ...
-39 |     cast!(2);
+38 |     cast!(2);
    |     --------- in this macro invocation
 
 error: aborting due to 2 previous errors