Enclose type in backticks for "non-exhaustive patterns" error

This makes the error style consistent with the convention in error messages.

Author: varkor

src/librustc_mir/hair/pattern/check_match.rs

@@ -234,7 +234,7 @@ impl<'a, 'tcx> MatchVisitor<'a, 'tcx> {
                 if !scrutinee_is_uninhabited {
                     // We know the type is inhabited, so this must be wrong
                     let mut err = create_e0004(self.tcx.sess, scrut.span,
-                                               format!("non-exhaustive patterns: type {} \
+                                               format!("non-exhaustive patterns: type `{}` \
                                                         is non-empty",
                                                        pat_ty));
                     span_help!(&mut err, scrut.span,

src/test/ui/error-codes/E0004-2.stderr

@@ -1,4 +1,4 @@
-error[E0004]: non-exhaustive patterns: type std::option::Option<i32> is non-empty
+error[E0004]: non-exhaustive patterns: type `std::option::Option<i32>` is non-empty
   --> $DIR/E0004-2.rs:14:11
    |
 LL |     match x { } //~ ERROR E0004

src/test/ui/issues/issue-3096-1.stderr

@@ -1,4 +1,4 @@
-error[E0004]: non-exhaustive patterns: type () is non-empty
+error[E0004]: non-exhaustive patterns: type `()` is non-empty
   --> $DIR/issue-3096-1.rs:12:11
    |
 LL |     match () { } //~ ERROR non-exhaustive

src/test/ui/issues/issue-3096-2.stderr

@@ -1,4 +1,4 @@
-error[E0004]: non-exhaustive patterns: type *const bottom is non-empty
+error[E0004]: non-exhaustive patterns: type `*const bottom` is non-empty
   --> $DIR/issue-3096-2.rs:15:11
    |
 LL |     match x { } //~ ERROR non-exhaustive patterns

src/test/ui/uninhabited/uninhabited-matches-feature-gated.stderr

@@ -4,7 +4,7 @@ error[E0004]: non-exhaustive patterns: `Err(_)` not covered
 LL |     let _ = match x {   //~ ERROR non-exhaustive
    |                   ^ pattern `Err(_)` not covered
 
-error[E0004]: non-exhaustive patterns: type &Void is non-empty
+error[E0004]: non-exhaustive patterns: type `&Void` is non-empty
   --> $DIR/uninhabited-matches-feature-gated.rs:20:19
    |
 LL |     let _ = match x {}; //~ ERROR non-exhaustive
@@ -16,7 +16,7 @@ help: ensure that all possible cases are being handled, possibly by adding wildc
 LL |     let _ = match x {}; //~ ERROR non-exhaustive
    |                   ^
 
-error[E0004]: non-exhaustive patterns: type (Void,) is non-empty
+error[E0004]: non-exhaustive patterns: type `(Void,)` is non-empty
   --> $DIR/uninhabited-matches-feature-gated.rs:23:19
    |
 LL |     let _ = match x {}; //~ ERROR non-exhaustive
@@ -28,7 +28,7 @@ help: ensure that all possible cases are being handled, possibly by adding wildc
 LL |     let _ = match x {}; //~ ERROR non-exhaustive
    |                   ^
 
-error[E0004]: non-exhaustive patterns: type [Void; 1] is non-empty
+error[E0004]: non-exhaustive patterns: type `[Void; 1]` is non-empty
   --> $DIR/uninhabited-matches-feature-gated.rs:26:19
    |
 LL |     let _ = match x {}; //~ ERROR non-exhaustive