resolve: Sort E0408 errors by Symbol str

Previously errors were sorted by Symbol index instead of the string. The
indexes are not the same between architectures because Symbols for
architecture extensions (e.g. x86 AVX or RISC-V d) are interned before
the source file is parsed. RISC-V's naming of extensions after single
letters led to it having errors sorted differently for test cases using
single letter variable names. Instead sort the errors by the Symbol
string so that it is stable across architectures.

Author: tblah

src/librustc_resolve/late.rs

@@ -1323,7 +1323,8 @@ impl<'a, 'b, 'ast> LateResolutionVisitor<'a, 'b, 'ast> {
 
         // 3) Report all missing variables we found.
         let mut missing_vars = missing_vars.iter_mut().collect::<Vec<_>>();
-        missing_vars.sort();
+        missing_vars.sort_by_key(|(sym, _err)| sym.as_str());
+
         for (name, mut v) in missing_vars {
             if inconsistent_vars.contains_key(name) {
                 v.could_be_path = false;

src/test/ui/or-patterns/mismatched-bindings-async-fn.stderr

@@ -1,11 +1,3 @@
-error[E0408]: variable `x` is not bound in all patterns
-  --> $DIR/mismatched-bindings-async-fn.rs:6:17
-   |
-LL | async fn a((x | s): String) {}
-   |             -   ^ pattern doesn't bind `x`
-   |             |
-   |             variable not in all patterns
-
 error[E0408]: variable `s` is not bound in all patterns
   --> $DIR/mismatched-bindings-async-fn.rs:6:13
    |
@@ -15,12 +7,12 @@ LL | async fn a((x | s): String) {}
    |             pattern doesn't bind `s`
 
 error[E0408]: variable `x` is not bound in all patterns
-  --> $DIR/mismatched-bindings-async-fn.rs:11:13
+  --> $DIR/mismatched-bindings-async-fn.rs:6:17
    |
-LL |     let x | s = String::new();
-   |         -   ^ pattern doesn't bind `x`
-   |         |
-   |         variable not in all patterns
+LL | async fn a((x | s): String) {}
+   |             -   ^ pattern doesn't bind `x`
+   |             |
+   |             variable not in all patterns
 
 error[E0408]: variable `s` is not bound in all patterns
   --> $DIR/mismatched-bindings-async-fn.rs:11:9
@@ -30,6 +22,14 @@ LL |     let x | s = String::new();
    |         |
    |         pattern doesn't bind `s`
 
+error[E0408]: variable `x` is not bound in all patterns
+  --> $DIR/mismatched-bindings-async-fn.rs:11:13
+   |
+LL |     let x | s = String::new();
+   |         -   ^ pattern doesn't bind `x`
+   |         |
+   |         variable not in all patterns
+
 error: aborting due to 4 previous errors
 
 For more information about this error, try `rustc --explain E0408`.

src/test/ui/span/issue-39698.stderr

@@ -8,16 +8,6 @@ LL |         T::T1(a, d) | T::T2(d, b) | T::T3(c) | T::T4(a) => { println!("{:?}
    |               |       pattern doesn't bind `a`
    |               variable not in all patterns
 
-error[E0408]: variable `d` is not bound in all patterns
-  --> $DIR/issue-39698.rs:10:37
-   |
-LL |         T::T1(a, d) | T::T2(d, b) | T::T3(c) | T::T4(a) => { println!("{:?}", a); }
-   |                  -          -       ^^^^^^^^   ^^^^^^^^ pattern doesn't bind `d`
-   |                  |          |       |
-   |                  |          |       pattern doesn't bind `d`
-   |                  |          variable not in all patterns
-   |                  variable not in all patterns
-
 error[E0408]: variable `b` is not bound in all patterns
   --> $DIR/issue-39698.rs:10:9
    |
@@ -38,6 +28,16 @@ LL |         T::T1(a, d) | T::T2(d, b) | T::T3(c) | T::T4(a) => { println!("{:?}
    |         |             pattern doesn't bind `c`
    |         pattern doesn't bind `c`
 
+error[E0408]: variable `d` is not bound in all patterns
+  --> $DIR/issue-39698.rs:10:37
+   |
+LL |         T::T1(a, d) | T::T2(d, b) | T::T3(c) | T::T4(a) => { println!("{:?}", a); }
+   |                  -          -       ^^^^^^^^   ^^^^^^^^ pattern doesn't bind `d`
+   |                  |          |       |
+   |                  |          |       pattern doesn't bind `d`
+   |                  |          variable not in all patterns
+   |                  variable not in all patterns
+
 error: aborting due to 4 previous errors
 
 For more information about this error, try `rustc --explain E0408`.